[HttpClient & ASP.NET Core] Fix metric description

[vishweshbankwar]

Fixes #4169

Changes

Please provide a brief description of the changes here.

For significant contributions please make sure you have completed the following items:

• Appropriate CHANGELOG.md updated for non-trivial changes
• Design discussion issue #
• Changes in public API reviewed

[cijothomas]

Thanks.

If we use the auto-generated semantic conventions, we wouldn't have to keep manual updates, right?

[codecov]

Codecov Report

Merging #4171 (1532469) into main (b549e12) will increase coverage by 0.04%.
The diff coverage is 100.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4171      +/-   ##
==========================================
+ Coverage   85.60%   85.64%   +0.04%     
==========================================
  Files         292      292              
  Lines       11467    11467              
==========================================
+ Hits         9816     9821       +5     
+ Misses       1651     1646       -5     

Impacted Files	Coverage Δ
...AspNetCore/Implementation/HttpInMetricsListener.cs	74.35% <100.00%> (ø)
...ementation/HttpHandlerMetricsDiagnosticListener.cs	95.00% <100.00%> (ø)
src/OpenTelemetry/BatchExportProcessor.cs	82.24% <0.00%> (-1.87%)	⬇️
...Telemetry/Internal/SelfDiagnosticsEventListener.cs	97.65% <0.00%> (+0.78%)	⬆️
...porter.OpenTelemetryProtocol/OtlpMetricExporter.cs	86.36% <0.00%> (+13.63%)	⬆️
...tation/OpenTelemetryProtocolExporterEventSource.cs	100.00% <0.00%> (+15.00%)	⬆️

[reyang]

Related to open-telemetry/semantic-conventions#897.

If we ever discovered any metrics description that is not a full sentence or misaligned with OpenMetrics convention, we should make the fix (both in the spec and implementations).