stream: add jitter to retry backoff in accordance with gRFC A6

[isgj]

Update the delay calculation to reflect the updated gRFC

Address #7514

RELEASE NOTES:

• client: update retry attempt backoff to apply jitter per updates to gRFC A6.

[linux-foundation-easycla]

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• ✅ login: isgj / name: Ismail Gjevori (df8dd0d, 81ae30b)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.00%. Comparing base (13d5a16) to head (df8dd0d).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #7869      +/-   ##
==========================================
- Coverage   82.04%   82.00%   -0.05%     
==========================================
  Files         375      375              
  Lines       37984    37984              
==========================================
- Hits        31165    31148      -17     
- Misses       5532     5540       +8     
- Partials     1287     1296       +9     

Files with missing lines	Coverage Δ
service_config.go	81.54% <100.00%> (ø)
stream.go	81.69% <100.00%> (+0.25%)	⬆️

... and 15 files with indirect coverage changes

---- 🚨 Try these New Features:

• Flaky Tests Detection - Detect and resolve failed and flaky tests

[aranjans]

@isgj Thanks for raising the PR. Can you add an end to end test to verify the same?

[aranjans]

Would be good if we could update the README of examples for retry feature.

[arjan-bal]

Would be good if we could update the README of examples for retry feature.

@aranjans can you point to the README and the example file that needs updating?

[isgj]

Would be good if we could update the README of examples for retry feature.

The README already points to the right gRFC https://github.com/grpc/grpc-go/blob/master/examples/features/retry/README.md?plain=1#L7

---

Can you add an end to end test to verify the same?

I see the tests at https://github.com/grpc/grpc-go/blob/master/test/retry_test.go.
Are you thinking about any specific test? I can try to add a test that checks the time when the retry happens, but that kind of test might be flaky

[aranjans]

@isgj Yes that's the correct reference to README.

Are you thinking about any specific test? I can try to add a test that checks the time when the retry happens, but that kind of test might be flaky
Ah yeah, that might be flaky. We could skip writing the test for that.

Overall this change LGTM, adding the @easwars as second reviewer to take a look.

[dfawley]

Thank you for the PR!