stats/opentelemetry: fix trace attributes message sequence numbers to start from 0

[yashykt]

As per https://github.com/grpc/proposal/blob/master/A72-open-telemetry-tracing.md sequence-number starts at 0.

RELEASE NOTES:

• stats/opentelemetry: fix trace attributes message sequence numbers to start from 0.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.25%. Comparing base (6bfa0ca) to head (6e6b327).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #8237      +/-   ##
==========================================
- Coverage   82.27%   82.25%   -0.02%     
==========================================
  Files         412      412              
  Lines       40491    40491              
==========================================
- Hits        33312    33305       -7     
- Misses       5824     5832       +8     
+ Partials     1355     1354       -1     

Files with missing lines	Coverage Δ
stats/opentelemetry/trace.go	87.50% <100.00%> (ø)

... and 23 files with indirect coverage changes

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