stats: Update documentation and examples to demonstrate enabling experimental metrics

[vinothkumarr227]

Fixes https://github.com/grpc/grpc-go/issues/8311

RELEASE NOTES:

Added documentation and code examples to demonstrate how to enable experimental metrics in gRPC-Go.

Updated example client and server code in [examples/features/opentelemetry]

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 82.31%. Comparing base (e5de1e2) to head (cd4419b). Report is 3 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #8388      +/-   ##
==========================================
- Coverage   82.33%   82.31%   -0.03%     
==========================================
  Files         413      413              
  Lines       40454    40430      -24     
==========================================
- Hits        33307    33278      -29     
+ Misses       5782     5779       -3     
- Partials     1365     1373       +8     

see 20 files with indirect coverage changes

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[arjan-bal]

Please merge the latest master branch to unblock the PR Validation test.

[arjan-bal]

The merge is not performed correctly. The PR diff is showing all the commits that were merged. Can you please reset and do a regular git merge origin/master?

[vinothkumarr227]

@arjan-bal I force-pushed after merging the latest master, and it seems the branch got closed automatically. Can you able to open this branch.

[arjan-bal]

There are 0 commits on the PR, so it can't be re-opened. If you can bring back the commits on this branch, I should be able to re-open it.