Phased out Grpc package for OTLP Exporter.

[Yun-Ting]

Fixes #3421.

Changes

• Removed Grpc package.
• Added HttpClient as a hard requirement for configuring GrpcChannelOptions.

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

[codecov]

Codecov Report

Merging #3885 (10f6a34) into main (a8b72df) will increase coverage by 0.00%.
The diff coverage is 100.00%.

❗ Current head 10f6a34 differs from pull request most recent head 982c1dc. Consider uploading reports for the commit 982c1dc to get more accurate results

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3885   +/-   ##
=======================================
  Coverage   87.34%   87.34%           
=======================================
  Files         279      279           
  Lines       10782    10783    +1     
=======================================
+ Hits         9417     9418    +1     
  Misses       1365     1365           

Impacted Files	Coverage Δ
...mentation/ExportClient/BaseOtlpGrpcExportClient.cs	83.33% <ø> (-0.88%)	⬇️
...TelemetryProtocol/OtlpExporterOptionsExtensions.cs	97.87% <100.00%> (+1.13%)	⬆️
src/OpenTelemetry/BatchExportProcessor.cs	82.24% <0.00%> (-1.87%)	⬇️
...ZPages/Implementation/ZPagesExporterEventSource.cs	62.50% <0.00%> (+6.25%)	⬆️

[alanwest]

I think the primary concern here is that this is probably a breaking change for some users. Consider .NET Framework users for whom things are working just fine today, but with this change they now have to configure the HttpClient for things to work. Worst part is that they'll only find this out at runtime.

[alanwest]

One idea we'd discussed in the past is to introduce separate OTLP/gRPC and OTLP/HTTP exporter packages. Something like

• OpenTelemetry.Exporter.OpenTelemetryProtocol.Grpc: This package would only depend on the new Grpc.Net.Client as you've done here. The benefit of it being a new package is that it won't break existing users.
• OpenTelemetry.Exporter.OpenTelemetryProtocol.Http: This could be done as a separate effort. Mostly just provides symmetry, but also reduces the number of transitive dependencies for users who don't want to use gRPC.