Add initial_node_count support to gke-node-pool

[sharabiani]

Support for initial_node_count added to gke-node-pool module.
Set it to provision the number of desired nodes right away after node-pool creation without the need for manual resize using cloud console.

The setting will be considered only when creating a node-pool and in the next deployments it will be ignored.

Manual tests:

• Added the initial_node_count setting to a node-pool in a blueprint
• Provisioned the blueprint
• Verified the number of provisioned nodes on Cloud Console

[ankitkinra]

If we ignore this setting update, then wouldn't our subsequent configurations using this node count be incorrect ?

Does this setting work with autoscaling ? How does this relate to static_node_count ?

[sharabiani]

@ankitkinra

If we ignore this setting update, then wouldn't our subsequent configurations using this node count be incorrect ?

It's recommended to ignore it for updates because if the node_pool resized manually, this setting will cause node_pool recreation: https://registry.terraform.io/providers/hashicorp/google/latest/docs/resources/container_node_pool.html#initial_node_count

Does this setting work with autoscaling ? How does this relate to static_node_count ?

node_count and initial_node_count cannot be set together:
https://github.com/hashicorp/terraform-provider-google/blob/6be57bdad382050af99b07d4b35ede995bfd97fe/google/services/container/resource_container_node_pool.go#L940
I added two precondition to control node_count and min/max total node count in autoscaling.