Fix severity mapping for OTLP Log Exporter

[cijothomas]

Towards #2482

[codecov]

Codecov Report

Merging #3177 (3053382) into main (4ff7278) will increase coverage by 0.20%.
The diff coverage is 85.71%.

@@            Coverage Diff             @@
##             main    #3177      +/-   ##
==========================================
+ Coverage   84.62%   84.82%   +0.20%     
==========================================
  Files         251      259       +8     
  Lines        9181     9322     +141     
==========================================
+ Hits         7769     7907     +138     
- Misses       1412     1415       +3     

Impacted Files	Coverage Δ
...etryProtocol/Implementation/LogRecordExtensions.cs	76.81% <85.71%> (+1.81%)	⬆️
...ter.ZPages/Implementation/ZPagesActivityTracker.cs	97.14% <0.00%> (-2.86%)	⬇️
...nTelemetry.Instrumentation.AspNet/AspNetMetrics.cs	100.00% <0.00%> (ø)
...ry.Instrumentation.AspNet/AspNetInstrumentation.cs	100.00% <0.00%> (ø)
...entation.AspNet/TracerProviderBuilderExtensions.cs	100.00% <0.00%> (ø)
...mentation.AspNet/MeterProviderBuilderExtensions.cs	100.00% <0.00%> (ø)
...umentation.AspNet/Implementation/HttpInListener.cs	88.31% <0.00%> (ø)
...ion.AspNet/Implementation/HttpInMetricsListener.cs	100.00% <0.00%> (ø)
...Implementation/AspNetInstrumentationEventSource.cs	76.92% <0.00%> (ø)
...rumentation.AspNet/AspNetInstrumentationOptions.cs	100.00% <0.00%> (ø)
... and 2 more