feat(propagation): baggage support and automatic propagation

[ZStriker19]

What does this PR do?
Following the spec here: https://www.w3.org/TR/baggage/ we implement baggage for the Ruby tracer. The otel drop in support will be added in a future PR.
Motivation:

Change log entry

Additional Notes:

How to test the change?

[github-actions]

👋 Hey @DataDog/ruby-guild, please fill "Change log entry" section in the pull request description.

If changes need to be present in CHANGELOG.md you can state it this way

**Change log entry**

Yes. A brief summary to be placed into the CHANGELOG.md

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**Change log entry**

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^{Visited at: 2025-02-20 19:01:38 UTC}

[datadog-datadog-prod-us1]

Datadog Report

Branch report: zachg/baggage_support
Commit report: 53087f8
Test service: dd-trace-rb

✅ 0 Failed, 20684 Passed, 1371 Skipped, 3m 7.51s Total Time

[pr-commenter]

Benchmarks

Benchmark execution time: 2025-03-12 19:13:38

Comparing candidate commit ec0d718 in PR branch zachg/baggage_support with baseline commit f710dac in branch master.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 31 metrics, 2 unstable metrics.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 99.57627% with 1 line in your changes missing coverage. Please review.

Project coverage is 97.75%. Comparing base (20886bc) to head (4dbe74b).
Report is 177 commits behind head on master.

Files with missing lines	Patch %	Lines
lib/datadog/tracing/distributed/baggage.rb	98.59%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4371      +/-   ##
==========================================
+ Coverage   97.74%   97.75%   +0.01%     
==========================================
  Files        1351     1353       +2     
  Lines       82697    82908     +211     
  Branches     4198     4222      +24     
==========================================
+ Hits        80831    81047     +216     
+ Misses       1866     1861       -5     

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