[SDK] Support TracerConfigurator updates

[dbarker]

Add support for updating the TracerConfigurator at runtime and provide an example.

The TracerProvider configuration includes the TracerConfigurator. SDKs may support updating the TracerConfigurator and resulting TracerConfig objects at runtime provided it is applied to previously created tracers. This feature allows dynamic enabling of tracers to turn tracing on or off without restarting the application.

https://opentelemetry.io/docs/specs/otel/trace/sdk/#configuration

The TracerProvider MAY provide methods to update the configuration. If configuration is updated (e.g., adding a SpanProcessor), the updated configuration MUST also apply to all already returned Tracers (i.e. it MUST NOT matter whether a Tracer was obtained from the TracerProvider before or after the configuration change).

Changes

• Add SDK TracerProvider::UpdateTracerConfigurator method and tests
• Change SDK Tracer::tracer_config_ to be an atomic shared pointer that will support dynamic updates including growth beyond the enabled bool.
• Add example showing runtime changes to the tracer configurator to enable/disable tracers.

For significant contributions please make sure you have completed the following items:

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

[codecov]

Codecov Report

❌ Patch coverage is 91.30435% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 82.01%. Comparing base (8fbe81e) to head (9b3d78b).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
sdk/src/trace/tracer_context.cc	60.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4065      +/-   ##
==========================================
+ Coverage   82.00%   82.01%   +0.02%     
==========================================
  Files         385      385              
  Lines       16030    16052      +22     
==========================================
+ Hits        13143    13163      +20     
- Misses       2887     2889       +2     

Files with missing lines	Coverage Δ
sdk/include/opentelemetry/sdk/trace/tracer.h	100.00% <ø> (ø)
...k/include/opentelemetry/sdk/trace/tracer_context.h	100.00% <ø> (ø)
sdk/src/trace/tracer.cc	87.35% <100.00%> (+1.24%)	⬆️
sdk/src/trace/tracer_provider.cc	91.38% <100.00%> (+1.80%)	⬆️
sdk/src/trace/tracer_context.cc	80.65% <60.00%> (-3.97%)	⬇️

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.