[otlp log exporter] Move logs extension methods to main otlp package

[vishweshbankwar]

Towards #4454
Design discussion issue #

Changes

This PR moves the logs extension methods to OpenTelemetry.Exporter.OpenTelemetryProtocol package and deletes OpenTelemetry.Exporter.OpenTelemetryProtocol.Logs .

Please provide a brief description of the changes here.

Merge requirement checklist

• CONTRIBUTING guidelines followed (nullable enabled, static analysis, etc.)
• Unit tests added/updated
• Appropriate CHANGELOG.md files updated for non-trivial changes
• Changes in public API reviewed (if applicable)

[codecov]

Codecov Report

Merging #4556 (1eda951) into main (9431d05) will decrease coverage by 0.01%.
The diff coverage is 87.50%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4556      +/-   ##
==========================================
- Coverage   85.20%   85.19%   -0.01%     
==========================================
  Files         320      320              
  Lines       12678    12678              
==========================================
- Hits        10802    10801       -1     
- Misses       1876     1877       +1     

Impacted Files	Coverage Δ
...lemetryProtocol/OtlpLogExporterHelperExtensions.cs	87.50% <87.50%> (ø)

... and 5 files with indirect coverage changes

[alanwest]

[23-06-07 11:58:20.116]Warning:[BuildCore.Build Document.LinkPhaseHandlerWithIncremental.ConceptualDocumentProcessor.Save] (src/OpenTelemetry.Exporter.OpenTelemetryProtocol/README.md#L56)Invalid file link:(~/src/OpenTelemetry.Exporter.OpenTelemetryProtocol.Logs/README.md).

[alanwest]

🥳 Finally! One OTLP exporter to rule them all!

[alanwest]

Oh, we should definitely add a changelog entry for this change.