Add configurable data plane log level

[bjee19]

Add Nginx error log level to NginxProxy.

Problem: Users would like to assign a log level for the data plane.

Solution: Add Nginx error log level to NginxProxy which allows users to set the error log level for Nginx.

Testing: Unit tests and manual testing.

Manual testing included

• Validating the enum values in the new ErrorLevel field in the NginxProxy resource.
• Deploying NGF, setting up the cafe-app, deploying an NginxProxy resource, and testing each of the possible log levels and checking that the nginx conf (the main.conf file and running nginx -T) in the nginx container was updated correctly.
• Checked that if the error level was not set in the NginxProxy resource, the nginx conf would be correctly updated back to the default of info log level.
• Tested that if a log level was set to something "beneath" notice such as the error level, after making changes which would result in notice log levels being outputted (such as deleting and re-applying cafe.yaml in the cafe example), no notice log levels are outputted.
• nginx -T correctly shows the main.conf configuration file being included in the nginx configuration.

Closes #901

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

All modified and coverable lines are covered by tests ✅

Project coverage is 89.35%. Comparing base (edbd856) to head (832acf9).
Report is 17 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2561      +/-   ##
==========================================
+ Coverage   89.34%   89.35%   +0.01%     
==========================================
  Files         100      101       +1     
  Lines        7630     7675      +45     
  Branches       50       50              
==========================================
+ Hits         6817     6858      +41     
- Misses        756      761       +5     
+ Partials       57       56       -1     

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