Add init container for setting up base config

[sjberman]

Problem: We are starting to introduce configuration options that exist in the main context. However, that configuration won't be written until the control plane writes it to nginx, meaning it doesn't exist on nginx startup. Therefore nginx uses its default configuration for a brief time, which is incorrect.

We want to be able to provide this configuration on startup.

Solution: Using an init container, we can mount a ConfigMap containing the dynamic base config, and copy it to the proper location in the filesystem before nginx starts. We can't mount the ConfigMap directly to the proper location because it would be read-only, preventing our control plane from writing to it.

This allows us to bootstrap the user config into nginx on startup, while also allowing our control plane to overwrite it if the user ever changes the config after the fact.

Removed logic that cleared out nginx files on startup because it would erase this bootstrap config, and it wasn't really needed since we delete nginx files when we write config anyway.

Also fixed an issue where the log level was not honored when no Gateway resources existed.

Testing: Verified that the log level is set properly on startup.

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.

Added an init container to bootstrap nginx config on startup.

[codecov]

Codecov Report

Attention: Patch coverage is 58.53659% with 17 lines in your changes missing coverage. Please review.

Project coverage is 88.56%. Comparing base (f8ab3e0) to head (2837992).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
cmd/gateway/commands.go	56.75%	15 Missing and 1 partial ⚠️
cmd/gateway/main.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2649      +/-   ##
==========================================
- Coverage   88.66%   88.56%   -0.11%     
==========================================
  Files         106      106              
  Lines        8141     8174      +33     
  Branches       50       50              
==========================================
+ Hits         7218     7239      +21     
- Misses        866      877      +11     
- Partials       57       58       +1     

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[bjee19]

👍