[Exporter.OpenTelemetryProtocol] Clients for profiling exporter

[Kielek]

Needed for https://github.com/open-telemetry/opentelemetry-dotnet-instrumentation/blob/main/docs/internal/continuous-profiler.md

Changes

1. Clients for Profiling exporters.
2. Expose internal OTLP Exporter API for OpenTelemetry.AutoInstrumetnation.

Profiling is highly experimental signal, but I would like to avoid making hard copies from this project into AutoInstrumentation.
For now, I decided to create here only direct clients. The exporter itself will be implemented in AutoInstrumentation.
I think that it is good compromise between reusability and possibility to make changes easily for Auto Instrumentation needs.

In the future, when the profiling will be closed to rc/ga state,I would expect to move more code to this project (Exporter).

Will be used by open-telemetry/opentelemetry-dotnet-instrumentation#3539

Other option

Alternative option is to make changes only in internals visible to and implement everything on the auto instrumentation side.

Merge requirement checklist

• CONTRIBUTING guidelines followed (license requirements, nullable enabled, static analysis, etc.)
• Unit tests added/updated
• [ ] Appropriate CHANGELOG.md files updated for non-trivial changes
• [ ] Changes in public API reviewed (if applicable)

[codecov]

Codecov Report

Attention: Patch coverage is 53.70370% with 25 lines in your changes missing coverage. Please review.

Project coverage is 86.16%. Comparing base (6250307) to head (7953493).
Report is 336 commits behind head on main.

Files with missing lines	Patch %	Lines
...ation/ExportClient/OtlpHttpProfilesExportClient.cs	12.50%	14 Missing ⚠️
...ation/ExportClient/OtlpGrpcProfilesExportClient.cs	41.66%	7 Missing ⚠️
...TelemetryProtocol/OtlpExporterOptionsExtensions.cs	84.61%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5759      +/-   ##
==========================================
+ Coverage   83.38%   86.16%   +2.78%     
==========================================
  Files         297      259      -38     
  Lines       12531    11204    -1327     
==========================================
- Hits        10449     9654     -795     
+ Misses       2082     1550     -532     

Flag	Coverage Δ
unittests	?
unittests-Project-Experimental	86.07% <53.70%> (?)
unittests-Project-Stable	86.16% <53.70%> (?)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
...TelemetryProtocol/OtlpExporterOptionsExtensions.cs	89.32% <84.61%> (-4.30%)	⬇️
...ation/ExportClient/OtlpGrpcProfilesExportClient.cs	41.66% <41.66%> (ø)
...ation/ExportClient/OtlpHttpProfilesExportClient.cs	12.50% <12.50%> (ø)

... and 215 files with indirect coverage changes

[vishweshbankwar]

@Kielek - What all things you would need to copy if we don't do this?

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