CP/DP Split: Add agent/nginx container and deployment

[sjberman]

Updating the nginx docker containers to build and include agent. Once agent is officially released, we can use the published binary instead of building.

Added a temporary nginx deployment to the helm chart to deploy a standalone nginx pod.

Added the basic gRPC server and agent API implementation to allow for the agent pod to connect to the control plane without errors.

Testing: Verified that the nginx/agent pod starts up successfully and connects to the control plane.

Closes #2839
Closes #2840

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 116 lines in your changes missing coverage. Please review.

Project coverage is 89.58%. Comparing base (6337c97) to head (08a740e).
Report is 6 commits behind head on change/control-data-plane-split.

Files with missing lines	Patch %	Lines
internal/mode/static/nginx/agent/command.go	0.00%	47 Missing ⚠️
internal/mode/static/nginx/agent/file.go	0.00%	24 Missing ⚠️
internal/mode/static/nginx/agent/grpc.go	0.00%	23 Missing ⚠️
internal/mode/static/manager.go	0.00%	15 Missing ⚠️
internal/mode/static/nginx/agent/agent.go	0.00%	7 Missing ⚠️

Additional details and impacted files

@@                         Coverage Diff                         @@
##           change/control-data-plane-split    #2957      +/-   ##
===================================================================
- Coverage                            89.74%   89.58%   -0.17%     
===================================================================
  Files                                  109      108       -1     
  Lines                                11150    11091      -59     
  Branches                                50       50              
===================================================================
- Hits                                 10007     9936      -71     
- Misses                                1083     1102      +19     
+ Partials                                60       53       -7     

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