feat: Move OTEL hooks to the SDK

[askpt]

Move OTEL hooks to the SDK

This pull request moves the OTEL hooks to the SDK, as discussed in the linked issue (#175). I also changed the unit tests to clean up some code. Finally, I moved the documentation.

Related Issues

Fixes #175

Notes

Implementation of Tracing and Metrics Hooks:

• src/OpenFeature/Hooks/MetricsConstants.cs: Introduced constants for metric names, descriptions, and attributes used in metrics collection.
• src/OpenFeature/Hooks/MetricsHook.cs: Implemented the MetricsHook class to capture metrics related to flag evaluations, including active counts, requests, successes, and errors.
• src/OpenFeature/Hooks/TracingConstants.cs: Added constants for tracing attributes and event names.
• src/OpenFeature/Hooks/TracingHook.cs: Implemented the TracingHook class to capture tracing information for flag evaluations, including key, variant, provider name, and exceptions.

Follow-up Tasks

• As mentioned in the Tracing Hook, we should use the new API method when we upgrade this repository is upgraded to dotnet 9. [1]
• We should remove any reference in the other repository and mark the Nuget package as deprecated.

[codecov]

Codecov Report

Attention: Patch coverage is 96.15385% with 3 lines in your changes missing coverage. Please review.

Project coverage is 85.72%. Comparing base (2774b0d) to head (52b47da).

Files with missing lines	Patch %	Lines
src/OpenFeature/Hooks/MetricsHook.cs	94.11%	0 Missing and 3 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #338      +/-   ##
==========================================
+ Coverage   85.17%   85.72%   +0.55%     
==========================================
  Files          36       38       +2     
  Lines        1477     1555      +78     
  Branches      150      157       +7     
==========================================
+ Hits         1258     1333      +75     
  Misses        188      188              
- Partials       31       34       +3     

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