[api-logs] LogRecordSeverity enum tweaks

[CodeBlanch]

Relates to #4433

Changes

• Incorporates some early feedback from @alanwest into the enum LogRecordSeverity definition.

Merge requirement checklist

• CONTRIBUTING guidelines followed (nullable enabled, static analysis, etc.)
• Unit tests added/updated

[codecov]

Codecov Report

Merging #4451 (3b7c4bb) into main (1b9290e) will decrease coverage by 0.27%.
The diff coverage is 0.00%.

❗ Current head 3b7c4bb differs from pull request most recent head e860c58. Consider uploading reports for the commit e860c58 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4451      +/-   ##
==========================================
- Coverage   84.09%   83.82%   -0.27%     
==========================================
  Files         311      312       +1     
  Lines       12329    12367      +38     
==========================================
- Hits        10368    10367       -1     
- Misses       1961     2000      +39     

Impacted Files	Coverage Δ
...nTelemetry.Api/Logs/LogRecordSeverityExtensions.cs	0.00% <0.00%> (ø)

... and 5 files with indirect coverage changes