Expose agent readiness endpoint on nginx port

[Anton-Kalpakchiev]

Currently, all services except the agent and tracker have their health and readiness endpoints exposed on their nginx port. The agent's readiness endpoint is exposed by the agent server (a different server, not the nginx server!). To reach consistency across services, the agent's readiness endpoint should be exposed by its nginx server (on the nginx port).

To expose the readiness endpoint on the nginx server, we can reroute any requests to the nginx /readiness API to the agentserver, exactly like we already do for the /health endpoint.

Tested locally by building the devcluster: (16000 is the nginx port)

root@9234fcfc2af8:/etc/kraken# curl http://localhost:16000/readiness
OKroot@9234fcfc2af8:/etc/kraken#