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.
• ps aux |grep nginx when inside the nginx container correctly showed nginx-debug processes.
• Deployed the cafe example and deleted it a few times and NGF still worked properly with no error logs in either container.

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 89.23%. Comparing base (edbd856) to head (9b6c854).
Report is 27 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2561      +/-   ##
==========================================
- Coverage   89.34%   89.23%   -0.11%     
==========================================
  Files         100      101       +1     
  Lines        7630     7667      +37     
  Branches       50       50              
==========================================
+ Hits         6817     6842      +25     
- Misses        756      768      +12     
  Partials       57       57              

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[bjee19]

Do we think this is needed? Also, if we should add a NGINX Plus in debug mode tab?

[bjee19]

@kate-osborn Should the wording on the comment be more strict to specify "require"?

I think it'd be fine to run NGINX in debug mode without NGINX error log level being debug, there'd be no point but I'd be fine with that. I can change this to something like "In order for this to be useful, NGINX error log level should be set to debug" or anything you suggest.

[bjee19]

would an nginx-plus in debug mode be beneficial to generate?

[bjee19]

Ready for review, still testing to make sure everything works with NGINX plus.

[sjberman]

Hm, this feels like it should be somewhere else...troubleshooting guide maybe?

[bjee19]

Closing this PR and moving to #2603