Do not allocate instrument options if possible in generated semconv packages

[MrAlias]

Avoid allocating instrument creation option if possible. If a user does not provide any options, use a static, read-only, file-level defined option slice. Otherwise, append to the user allocated slice the description and unit options.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.9%. Comparing base (9b6585a) to head (3d159d3).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #7328   +/-   ##
=====================================
  Coverage   82.9%   82.9%           
=====================================
  Files        267     267           
  Lines      24997   24997           
=====================================
+ Hits       20743   20744    +1     
+ Misses      3878    3877    -1     
  Partials     376     376           

see 1 file with indirect coverage changes

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