Add glog slog handler

[pdabelf5]

Proposed changes

• add basic slog handler for glog formatting
• add ability to add logger to a context

To create a new slog based logger using the glog handler you can use code similar to:

import nic_glog "github.com/nginxinc/kubernetes-ingress/internal/logger/glog"

programLevel := new(slog.LevelVar) // Info by default
l := slog.New(nic_glog.New(os.Stdout, &nic_glog.Options{Level: programLevel}))
slog.SetDefault(l)

# To adjust the log level
programLevel.Set(slog.LevelDebug)

To attach the logger to a context you can use:

ctx := nic_logger.ContextWithLogger(context.Background(), slog.New(nic_glog.New(os.Stdout, nil)))

To retrieve the logger from the context use

l := nic_logger.LoggerFromContext(ctx)
l.Warn("my warning log")

slog does not provide Fatal & Trace log levels by default. These have been added to the glog handler but the following syntax is needed to log using these levels

l.Log(context.Background(), LevelTrace, "test")
l.Log(context.Background(), LevelFatal, "test")
os.Exit(1)

Note: The l.Log(context.Background(), LevelFatal, "test") implementation needs to call os.Exit() as the Fatal level does not exit itself.

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

Attention: Patch coverage is 82.14286% with 10 lines in your changes missing coverage. Please review.

Project coverage is 53.30%. Comparing base (c099abe) to head (146b6a5).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
internal/logger/logger.go	0.00%	6 Missing ⚠️
internal/logger/glog/handler.go	92.00%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6474      +/-   ##
==========================================
+ Coverage   53.21%   53.30%   +0.09%     
==========================================
  Files          85       87       +2     
  Lines       16016    16074      +58     
==========================================
+ Hits         8523     8569      +46     
- Misses       7085     7097      +12     
  Partials      408      408              

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[jjngx]

it looks great! 🚀