feat: Support levelled logs using slog in go module.

[thomaspoignant]

Description

This PR adds support to levelled logs using the new go logging capabilities slog.

Using slog is optional but recommended. It keeps supporting the log.logger interface.
To use this new way of logging inside add your slog logger in the LevelledLogger field in the configuration.

Closes issue(s)

Resolves #1713

Checklist

• I have tested this code
• I have added unit test to cover this code
• I have updated the documentation (README.md and /website/docs)
• I have followed the contributing guide

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[codecov]

Codecov Report

Attention: Patch coverage is 85.86957% with 13 lines in your changes missing coverage. Please review.

Project coverage is 86.96%. Comparing base (a2e12be) to head (8631b44).

Files	Patch %	Lines
internal/cache/in_memory_cache.go	20.00%	4 Missing ⚠️
exporter/gcstorageexporter/exporter.go	33.33%	2 Missing ⚠️
exporter/s3exporter/exporter.go	50.00%	2 Missing ⚠️
retriever/manager.go	66.66%	1 Missing and 1 partial ⚠️
cmd/relayproxy/service/gofeatureflag.go	0.00%	1 Missing ⚠️
exporter/s3exporterv2/exporter.go	66.66%	1 Missing ⚠️
feature_flag.go	91.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1955      +/-   ##
==========================================
+ Coverage   86.88%   86.96%   +0.08%     
==========================================
  Files          98       98              
  Lines        3553     3599      +46     
==========================================
+ Hits         3087     3130      +43     
- Misses        358      359       +1     
- Partials      108      110       +2     

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[sonarcloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
0.2% Duplication on New Code

See analysis details on SonarCloud