Add skeleton for gRPC Commander Service

[kate-osborn]

Fixes #377

Adds a gRPC server and the skeleton for the Commander service.

The Commander service implementation is a version of this example. It's the least amount of code required to get the agent and control plane to communicate without errors. The Commander code is for demo purposes only and will change once I add the config push and registration functionality. The agent requests exercise both the CommandChannel and Upload functions but not the Download function. To exercise the Download function, I would have to add a fair amount of code that would just be removed later. I think the current functionality is enough to demonstrate that the agent and control plane can communicate.

The purpose of this PR is to show the general skeleton of the server and Commander service and get early feedback before adding a bunch of business logic.

Here are some of the logs of the nginx-gateway container showing the agent messages:

{"level":"info","ts":"2023-02-02T22:58:50Z","logger":"commanderService","msg":"Commander CommandChannel"}
{"level":"info","ts":"2023-02-02T22:58:50Z","logger":"commanderService","msg":"ignoring command","command data type":"*proto.Command_EventReport"}
{"level":"info","ts":"2023-02-02T22:58:50Z","logger":"commanderService","msg":"ignoring command","command data type":"*proto.Command_EventReport"}
{"level":"info","ts":"2023-02-02T22:58:50Z","logger":"commanderService","msg":"ignoring command","command data type":"*proto.Command_DataplaneStatus"}
{"level":"info","ts":"2023-02-02T22:58:50Z","logger":"commanderService","msg":"Received a connection request from an agent","data":"version:\"v2.22.1\" display_name:\"nginx-gateway-d8d6d5477-sl6fh\" updated:<seconds:1675196537 > system_uid:\"badd8659-67fb-3525-a40f-b25a6af4b7cd\" agent_details:<features:\"features_registration\" features:\"features_nginx-config\" features:\"features_nginx-ssl-config\" features:\"features_nginx-counting\" features:\"features_nginx-config-async\" features:\"features_metrics\" features:\"features_metrics-throttle\" features:\"features_dataplane-status\" features:\"features_process-watcher\" features:\"features_file-watcher\" features:\"features_activity-events\" features:\"features_agent-api\" > "}
{"level":"info","ts":"2023-02-02T22:58:50Z","logger":"commanderService","msg":"Commander Upload requested"}
{"level":"info","ts":"2023-02-02T22:58:50Z","logger":"commanderService","msg":"Received chunk from upload channel","chunk":REDACTED}
{"level":"info","ts":"2023-02-02T22:58:50Z","logger":"commanderService","msg":"Received chunk from upload channel","chunk":"<nil>"}
{"level":"info","ts":"2023-02-02T22:58:50Z","logger":"commanderService","msg":"Commander Upload completed"}
{"level":"info","ts":"2023-02-02T22:58:50Z","logger":"commanderService","msg":"ignoring command","command data type":"*proto.Command_EventReport"}
{"level":"info","ts":"2023-02-02T22:58:50Z","logger":"commanderService","msg":"ignoring command","command data type":"*proto.Command_EventReport"}
{"level":"info","ts":"2023-02-02T22:59:20Z","logger":"commanderService","msg":"ignoring command","command data type":"*proto.Command_DataplaneStatus"}

and here are some of the logs of the nginx-with-agent container that show the successful connection to the control plane:

time="2023-02-02T22:58:50Z" level=info msg="Commander received meta:<timestamp:<seconds:1675378730 nanos:417763900 > message_id:\"84cc33a2-7505-4ea6-95c7-c7323e8cae0c\" > agent_connect_response:<agent_config:<configs:<meta:<timestamp:<seconds:1675378730 nanos:417748700 > message_id:\"84cc33a2-7505-4ea6-95c7-c7323e8cae0c\" > configs:<system_id:\"badd8659-67fb-3525-a40f-b25a6af4b7cd\" nginx_id:\"b636d4376dea15405589692d3c5d3869ff3a9b26b0e7bb4bb1aa7e658ace1437\" > > > status:<statusCode:CONNECT_OK message:\"Connected\" > > , <nil>"
127.0.0.1 - - [02/Feb/2023:22:58:50 +0000] "HEAD /api HTTP/1.1" 200 0 "-" "Go-http-client/1.1" "-"
time="2023-02-02T22:58:50Z" level=info msg="config command &{agent_config:<configs:<meta:<timestamp:<seconds:1675378730 nanos:417748700 > message_id:\"84cc33a2-7505-4ea6-95c7-c7323e8cae0c\" > configs:<system_id:\"badd8659-67fb-3525-a40f-b25a6af4b7cd\" nginx_id:\"b636d4376dea15405589692d3c5d3869ff3a9b26b0e7bb4bb1aa7e658ace1437\" > > > status:<statusCode:CONNECT_OK message:\"Connected\" > }"
time="2023-02-02T22:58:50Z" level=info msg="Upload: Sending data chunk data 0 (messageId=29fa97af-11e8-46ee-a1a8-085f95ffe360)"
time="2023-02-02T22:58:50Z" level=info msg="Upload sending done 29fa97af-11e8-46ee-a1a8-085f95ffe360 (chunks=1)"

The nginx-with-agent container is currently running as a third container inside the nginx-gateway Pod, alongside the nginx and nginx-gateway containers. Once #378 and #379 are complete, I'll remove the nginx container.