[Deprecation] Deprecate experimental semantic conventions (#1742)

[marcalff]

Fixes #1742

Changes

Announce the deprecation of experimental semantic conventions in the CHANGELOG.

Announce the deprecation of a global hash function.

This function is not declared in the opentelemetry namespace, and as such, is considered potentially harmful to the application code.

This function is not part of the opentelemetry-cpp API, but rather an implementation artifact of experimental semantic conventions that leaked and got exposed to the application code.

• CHANGELOG.md updated for non-trivial changes
• Unit tests have been added
• Changes in public API reviewed

[codecov]

Codecov Report

Merging #1744 (c3bf495) into main (a220ac4) will decrease coverage by 0.02%.
The diff coverage is n/a.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1744      +/-   ##
==========================================
- Coverage   85.79%   85.77%   -0.01%     
==========================================
  Files         171      171              
  Lines        5212     5212              
==========================================
- Hits         4471     4470       -1     
- Misses        741      742       +1     

Impacted Files	Coverage Δ
sdk/src/trace/batch_span_processor.cc	90.63% <0.00%> (-0.78%)	⬇️