[otlp] Add Grpc vendored code

[rajkumar-rangaraj]

Fixes Part of #5730
Design discussion issue #

Changes

Please provide a brief description of the changes here.

Copied the following files from grpc-dotnet, these are needed to check the status and retry. These files are enough to remove the complete dependencies on Grpc packages.

• Few Methods from https://github.com/grpc/grpc-dotnet/blob/v2.66.0/src/Grpc.Net.Client/Internal/GrpcProtocolHelpers.cs
• https://github.com/grpc/grpc-dotnet/blob/v2.66.0/src/Shared/TrailingHeadersHelpers.cs
• https://github.com/grpc/grpc-dotnet/blob/v2.66.0/src/Grpc.Core.Api/StatusCode.cs
• https://github.com/grpc/grpc-dotnet/blob/v2.66.0/src/Grpc.Core.Api/Status.cs

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 0% with 74 lines in your changes missing coverage. Please review.

Project coverage is 84.11%. Comparing base (2ae01a7) to head (88b7561).

Files with missing lines	Patch %	Lines
...mentation/ExportClient/Grpc/GrpcProtocolHelpers.cs	0.00%	43 Missing ⚠️
...rotocol/Implementation/ExportClient/Grpc/Status.cs	0.00%	21 Missing ⚠️
...tation/ExportClient/Grpc/TrailingHeadersHelpers.cs	0.00%	10 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5981      +/-   ##
==========================================
- Coverage   84.50%   84.11%   -0.40%     
==========================================
  Files         271      274       +3     
  Lines       12355    12429      +74     
==========================================
+ Hits        10441    10455      +14     
- Misses       1914     1974      +60     

Flag	Coverage Δ
unittests-Project-Experimental	84.09% <0.00%> (-0.23%)	⬇️
unittests-Project-Stable	84.02% <0.00%> (-0.48%)	⬇️

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

Files with missing lines	Coverage Δ
...tation/ExportClient/Grpc/TrailingHeadersHelpers.cs	0.00% <0.00%> (ø)
...rotocol/Implementation/ExportClient/Grpc/Status.cs	0.00% <0.00%> (ø)
...mentation/ExportClient/Grpc/GrpcProtocolHelpers.cs	0.00% <0.00%> (ø)

... and 2 files with indirect coverage changes