KNOX-2962 - Knox readiness check gateway-status endpoint should return the list of topologies for which it is waiting for

[zeroflag]

What changes were proposed in this pull request?

The gateway-status requests returns the list of pending topologies.

How was this patch tested?

Added health topology:

<topology>
    <gateway>
        <provider>
            <role>authentication</role>
            <name>Anonymous</name>
            <enabled>true</enabled>
        </provider>
    </gateway>
    <service>
        <role>HEALTH</role>
    </service>
</topology>

and 2 invalid descriptors: test.json and test2.json

$ curl -vk https://localhost:8443/gateway/health/v1/gateway-status

Output

< HTTP/1.1 200 OK
< Date: Mon, 09 Oct 2023 10:36:50 GMT
< Cache-Control: must-revalidate,no-cache,no-store
< Content-Type: text/plain;charset=iso-8859-1
< Content-Length: 23
< 
PENDING: [test2, test]

[smolnar82]

LGTM