[otlp] Add Retry Handler

[vishweshbankwar]

Towards #1779
Design discussion issue #

Changes

Adds a retry transmission handler for retrying transient errors. It covers both http and grpc protocol.

Planning to do a follow up PR which will add the ability to opt-in for retries via an experimental environment variable.

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 78.26087% with 5 lines in your changes are missing coverage. Please review.

Project coverage is 84.81%. Comparing base (6250307) to head (2d756ae).
Report is 127 commits behind head on main.

❗ Current head 2d756ae differs from pull request most recent head 572f529. Consider uploading reports for the commit 572f529 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5433      +/-   ##
==========================================
+ Coverage   83.38%   84.81%   +1.42%     
==========================================
  Files         297      284      -13     
  Lines       12531    12206     -325     
==========================================
- Hits        10449    10352      -97     
+ Misses       2082     1854     -228     

Flag	Coverage Δ
unittests	?
unittests-Solution-Experimental	84.78% <78.26%> (?)
unittests-Solution-Stable	84.74% <78.26%> (?)

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

Files	Coverage Δ
...rotocol/Implementation/Transmission/RetryHelper.cs	100.00% <100.00%> (ø)
...ansmission/OtlpExporterRetryTransmissionHandler.cs	80.00% <80.00%> (ø)
...yProtocol/Implementation/ExportClient/OtlpRetry.cs	88.57% <40.00%> (+5.81%)	⬆️

... and 60 files with indirect coverage changes

[vishweshbankwar]

@alanwest - I did not quite understand the significance of this test. It was testing that we would retry if the deadline is not set and server responds with a very high delay. We should not run in to this case as we would always have the deadline set, let me know if I am missing something here.