Support sending chunked files to agent

[sjberman]

Problem: If nginx.conf files are too large, they can't be sent over the existing gRPC stream to agent.

Solution: Agent has added an API and helper function to send files in chunks if over a certain size limit. Our controller will implement this API for agent to call when in this condition.

Testing: Verified that files over the threshold are chunked.

Closes #3315

Checklist

Before creating a PR, run through this checklist and mark each as complete.

• I have read the CONTRIBUTING doc
• I have added tests that prove my fix is effective or that my feature works
• I have checked that all unit tests pass after adding my changes
• I have updated necessary documentation
• I have rebased my branch onto main
• I will ensure my PR is targeting the main branch and pulling from my branch from my own fork

Release notes

If this PR introduces a change that affects users and needs to be mentioned in the release notes,
please add a brief note that summarizes the change.

[codecov]

Codecov Report

Attention: Patch coverage is 87.34177% with 10 lines in your changes missing coverage. Please review.

Project coverage is 86.73%. Comparing base (2a330c8) to head (3b61e69).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
internal/mode/static/nginx/agent/file.go	85.71%	7 Missing and 3 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3390      +/-   ##
==========================================
- Coverage   86.79%   86.73%   -0.06%     
==========================================
  Files         129      129              
  Lines       14862    14928      +66     
  Branches       62       62              
==========================================
+ Hits        12899    12948      +49     
- Misses       1816     1828      +12     
- Partials      147      152       +5     

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