Add a derive crate to allow deriving conversions into common types

[Sufflope]

Moved from open-telemetry/opentelemetry-rust#1686

Changes

Implement derive macros to convert user types into common Key/Value related types.

See open-telemetry/opentelemetry-rust#1685

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

Attention: Patch coverage is 98.79518% with 2 lines in your changes missing coverage. Please review.

Project coverage is 59.7%. Comparing base (56a6f45) to head (058a70f).
Report is 38 commits behind head on main.

Files with missing lines	Patch %	Lines
...emetry-derive/opentelemetry-derive-impl/src/lib.rs	98.1%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##            main    #112     +/-   ##
=======================================
+ Coverage   52.3%   59.7%   +7.4%     
=======================================
  Files         38      41      +3     
  Lines       4967    5940    +973     
=======================================
+ Hits        2598    3551    +953     
- Misses      2369    2389     +20     

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[Sufflope]

I changed the intra-doc links to common types to direct links to docs.rs to avoid adding the opentelemetry crate to dependencies, which would then be added to users' projects dependency tree in the workspace version, possibly another version than the one they use.

The two uncovered lines are weird false negatives, is it blocking?