feat: better diagnostic logging configuration

[seemk]

• New optional option to start: logLevel. Setting it configures the OTel diagnostic console logger with the specified log level.
• Can also be set via OTEL_LOG_LEVEL. Previously this only set the log level but did not create the logging pipeline.

Fixes:

• Create an shortcut to enabling diagnostics logger #293
• Docs: explain how diag log level and OTEL_LOG_LEVEL env variable interact #598

[codecov-commenter]

Codecov Report

Base: 83.69% // Head: 84.10% // Increases project coverage by +0.40% 🎉

Coverage data is based on head (009f31a) compared to base (c141e58).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #605      +/-   ##
==========================================
+ Coverage   83.69%   84.10%   +0.40%     
==========================================
  Files          28       28              
  Lines        1141     1170      +29     
  Branches      255      265      +10     
==========================================
+ Hits          955      984      +29     
  Misses        186      186              

Impacted Files	Coverage Δ
src/start.ts	100.00% <100.00%> (ø)
src/utils.ts	97.18% <100.00%> (+1.34%)	⬆️

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