[inmemory-logs] Expose LoggerProviderBuilder extension

[CodeBlanch]

Relates to #4433

Changes

• Exposes the LoggerProviderBuilder.AddInMemoryExporter extension

Merge requirement checklist

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

[codecov]

Codecov Report

Merging #4584 (d617576) into main (09399d8) will not change coverage.
The diff coverage is n/a.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4584   +/-   ##
=======================================
  Coverage   85.12%   85.12%           
=======================================
  Files         320      320           
  Lines       12679    12679           
=======================================
  Hits        10793    10793           
  Misses       1886     1886           

Impacted Files	Coverage Δ
...rter.InMemory/InMemoryExporterLoggingExtensions.cs	66.66% <ø> (ø)

... and 2 files with indirect coverage changes