feat: Add support for OpenAI client library for .NET

[tippmar-nr]

BEGIN_COMMIT_OVERRIDE
feat: Add AI Monitoring instrumentation for OpenAI and Azure.AI.OpenAI (#2987)
END_COMMIT_OVERRIDE

Description

Adds instrumentation for the OpenAI client library for .NET, version 2.0.0 and later. Note that this feature also supports Azure.AI.OpenAI version 2.0.0 and later.

Text chat completions for the following methods are instrumented:
CompleteChatAsync()
CompleteChat()

Includes unit and integration tests.

Thanks to @harrykimpel for the initial implementation work!

Author Checklist

• Unit tests, Integration tests, and Unbounded tests completed
• Performance testing completed with satisfactory results (if required)

Reviewer Checklist

• Perform code review
• Pull request was adequately tested (new/existing tests, performance tests)

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 80.00000% with 15 lines in your changes missing coverage. Please review.

Project coverage is 82.19%. Comparing base (19e8387) to head (7d84ed6).

Files with missing lines	Patch %	Lines
...sions/Llm/Bedrock/BedrockLlmModelTypeExtensions.cs	0.00%	15 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2987      +/-   ##
==========================================
+ Coverage   82.17%   82.19%   +0.01%     
==========================================
  Files         473      475       +2     
  Lines       30391    30450      +59     
  Branches     3392     3407      +15     
==========================================
+ Hits        24975    25027      +52     
- Misses       4617     4621       +4     
- Partials      799      802       +3     

Flag	Coverage Δ
Agent	83.16% <80.00%> (+0.01%)	⬆️
Profiler	73.13% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
...sions/NewRelic.Agent.Extensions/Llm/EventHelper.cs	99.25% <100.00%> (-0.75%)	⬇️
...ensions/Llm/OpenAi/OpenAiHeaderDictionaryHelper.cs	100.00% <100.00%> (ø)
...sions/Llm/Bedrock/BedrockLlmModelTypeExtensions.cs	0.00% <0.00%> (ø)

... and 2 files with indirect coverage changes