CP/DP Split: track agent connections

[sjberman]

Added the following:

• middleware to extract IP address of agent and store it in the grpc context
• link the agent's hostname to its IP address when connecting and track it
• use this linkage to pause the Subscription until the agent registers itself, then proceeding

This logic is subject to change as we enhance this (like tracking auth token instead of IP address).

Testing: Verified that connections are mapped properly between CreateConnection and Subscribe calls and that the subscription waits properly. Scaled nginx to multiple replicas and saw all connections.

Closes #2851

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 186 lines in your changes missing coverage. Please review.

Project coverage is 88.61%. Comparing base (6337c97) to head (4e415c4).
Report is 8 commits behind head on change/control-data-plane-split.

Files with missing lines	Patch %	Lines
internal/mode/static/nginx/agent/command.go	0.00%	63 Missing ⚠️
...static/nginx/agent/grpc/interceptor/interceptor.go	0.00%	43 Missing ⚠️
internal/mode/static/nginx/agent/grpc/grpc.go	0.00%	38 Missing ⚠️
...ternal/mode/static/nginx/agent/grpc/connections.go	0.00%	19 Missing ⚠️
internal/mode/static/nginx/agent/agent.go	0.00%	7 Missing ⚠️
internal/mode/static/nginx/agent/file.go	0.00%	6 Missing ⚠️
internal/mode/static/manager.go	0.00%	5 Missing ⚠️
...al/mode/static/nginx/agent/grpc/context/context.go	0.00%	5 Missing ⚠️

Additional details and impacted files

@@                         Coverage Diff                         @@
##           change/control-data-plane-split    #2970      +/-   ##
===================================================================
- Coverage                            89.74%   88.61%   -1.13%     
===================================================================
  Files                                  109      111       +2     
  Lines                                11150    11212      +62     
  Branches                                50       50              
===================================================================
- Hits                                 10007     9936      -71     
- Misses                                1083     1223     +140     
+ Partials                                60       53       -7     

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[kate-osborn]

I know a lot of this code will end up changing, but are there any files or components you feel confident in that we can write unit tests for now?

[sjberman]

I know a lot of this code will end up changing, but are there any files or components you feel confident in that we can write unit tests for now?

Honestly, not really. I think the meat of these functions will change as we implement the next few stories.