Proposal: Allocator service to return 400+ http status for failure

[pooneh-m]

Is your feature request related to a problem? Please describe.
When allocating a game server, if there is an issue that the game server cannot be allocated, the allocator service response is 200 http status with the state of either "unallocated" or "contention". For a RESTful API, the http status represents the status of the result and receiving 200 for an unsuccessful response is contradicting. In kubernetes world, status is a good representation of the state of a CRD, but this is not be the standard for REST APIs.

Describe the solution you'd like
The allocation REST API should return a meaningful http status in case of failure instead of 200. My proposal is to return 429 http status (ResourceExhausted grpc code) for unallocated state and 409 for contention.

[markmandel]

So I didn't realise that gRPC has codes that translate to HTTP Status codes through the grpc-gateway.

I think that was the blocking issue in my mind - but now I realise this, I'm 100% on board.