Stackdriver - use upstream otel-rust dependencies from last common commit

[ivan-brko]

Fixes

Fixes compile issues for opentelemetry-stackdriver.
Using the upstream commit just before opentelemetry-stackdriver was removed from the core repo to contrib (6175c3f1edf8510d947a6543c68512408ae15836).

@djc sorry for the constant spamming, hope I got it right this time, the crate is building without any issues. opentelemetry-semantic-conventions was set to a crate version, but it also had to be set to the commit.

Changes

Temporarily depend on specific commit in the upstream repository, until new versions of those crates are released. This allows the library to be built and new features developed in the meantime.
This was proposed in #8.

Merge requirement checklist

• CONTRIBUTING guidelines followed
• Unit tests added/updated (if applicable)
• Appropriate CHANGELOG.md files updated for non-trivial, user-facing changes
• Changes in public API reviewed (if applicable)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (a3e0d18) 40.4% compared to head (d7d38dc) 40.4%.

Additional details and impacted files

@@          Coverage Diff          @@
##            main     #24   +/-   ##
=====================================
  Coverage   40.4%   40.4%           
=====================================
  Files         12      12           
  Lines       1277    1279    +2     
=====================================
+ Hits         516     517    +1     
- Misses       761     762    +1     

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