docs: mention node priority (#10443)

Signed-off-by: Navendu Pottekkat <navendu@apache.org>

docs/en/latest/admin-api.md

@@ -890,7 +890,7 @@ In addition to the equalization algorithm selections, Upstream also supports pas
 | Parameter                   | Required                                                         | Type                          | Description                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  | Example                                                                                                                                    |
 |-----------------------------|------------------------------------------------------------------|-------------------------------|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|--------------------------------------------------------------------------------------------------------------------------------------------|
 | type                        | False                                                            | Enumeration                   | Load balancing algorithm to be used, and the default value is `roundrobin`.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |                                                                                                                                            |
-| nodes                       | True, can't be used with `service_name`                          | Node                          | IP addresses (with optional ports) of the Upstream nodes represented as a hash table or an array. In the hash table, the key is the IP address and the value is the weight of the node for the load balancing algorithm. For hash table case, if the key is IPv6 address with port, then the IPv6 address must be quoted with square brackets. In the array, each item is a hash table with keys `host`, `weight`, and the optional `port` and `priority`. Empty nodes are treated as placeholders and clients trying to access this Upstream will receive a 502 response.                                                   | `192.168.1.100:80`, `[::1]:80`                                                                                                             |
+| nodes                       | True, can't be used with `service_name`                          | Node                          | IP addresses (with optional ports) of the Upstream nodes represented as a hash table or an array. In the hash table, the key is the IP address and the value is the weight of the node for the load balancing algorithm. For hash table case, if the key is IPv6 address with port, then the IPv6 address must be quoted with square brackets. In the array, each item is a hash table with keys `host`, `weight`, and the optional `port` and `priority` (defaults to `0`). Nodes with lower priority are used only when all nodes with a higher priority are tried and are unavailable. Empty nodes are treated as placeholders and clients trying to access this Upstream will receive a 502 response.                                                   | `192.168.1.100:80`, `[::1]:80`                                                                                                             |
 | service_name                | True, can't be used with `nodes`                                 | String                        | Service name used for [service discovery](discovery.md).                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     | `a-bootiful-client`                                                                                                                        |
 | discovery_type              | True, if `service_name` is used                                  | String                        | The type of service [discovery](discovery.md).                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               | `eureka`                                                                                                                                   |
 | hash_on                     | False                                                            | Auxiliary                     | Only valid if the `type` is `chash`. Supports Nginx variables (`vars`), custom headers (`header`), `cookie` and `consumer`. Defaults to `vars`.                                                                                                                                                                                                                                                                                                                                                                                                                                                                              |                                                                                                                                            |