Remove deprecated log level parameters

[AlexFenlon]

Proposed changes

• fix nil pointer when glog is removed in flags.go to prepare for full glog removal in the healthcheck package soon by removing a check forlogtostderr and include_year flags as logtostderr was included with glog and include_year has been removed.
• update old -v= to -log-level= as it was only used for glog which has now been switched out and -v= has no longer been used since Add LogLevel & LogFormat flags #6520

What logtostderr flag was doing in glog

logtostderr (bool, default=false)
Log messages to stderr instead of logfiles.

Helm-chart will need to be updated to v2.0.0 as we have a breaking change changing from -v to -log-level so this needs to be done

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

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 53.26%. Comparing base (297aa1b) to head (f6ec21b).
Report is 5 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6620      +/-   ##
==========================================
+ Coverage   53.24%   53.26%   +0.01%     
==========================================
  Files          87       87              
  Lines       16263    16257       -6     
==========================================
  Hits         8660     8660              
+ Misses       7188     7182       -6     
  Partials      415      415              

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[jjngx]

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[github-actions]

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[ADubhlaoich]

LGTM, though the PR is largely not docs-based.

[j1m-ryan]

can you update the docs here https://github.com/nginxinc/kubernetes-ingress/blob/main/site/content/logging-and-monitoring/logging.md?