Bump OTLP proto files to 1.2.0

[Kielek]

Fixes N/A
Design discussion issue N/A

Changes

Bump OTLP proto files to 1.2.0.

Support for OTLP new features can be handled separately, as for #5215

• Indicate if a Span's parent or link is remote using 2 bit flag. Indicate if a span's parent or link is remote using 2 bit flag as described in OTEP 0182 opentelemetry-proto#484
• Add metric.metadata for supporting additional metadata on metrics Add metric.metadata for supporting additional metadata on metrics opentelemetry-proto#514

Done while working on test update for auto-instrumentation.

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

All modified and coverable lines are covered by tests ✅

Project coverage is 85.57%. Comparing base (6250307) to head (ae1d8bd).
Report is 168 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5516      +/-   ##
==========================================
+ Coverage   83.38%   85.57%   +2.18%     
==========================================
  Files         297      289       -8     
  Lines       12531    12588      +57     
==========================================
+ Hits        10449    10772     +323     
+ Misses       2082     1816     -266     

Flag	Coverage Δ
unittests	?
unittests-Solution-Experimental	85.47% <ø> (?)
unittests-Solution-Stable	85.49% <ø> (?)

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see 65 files with indirect coverage changes