Add OpenTelemetry Global Detection to the Agent

[JacksonWeber]

This pull request enhances the Application Insights agent loader to proactively detect and report conflicts with existing OpenTelemetry global providers before attaching the agent. It introduces a new diagnostic message for OpenTelemetry conflicts and adds comprehensive unit tests to ensure correct detection and logging of these scenarios.

OpenTelemetry conflict detection and diagnostics:

• Added a new _detectOpenTelemetryGlobals method in AgentLoader to check for global OpenTelemetry TracerProvider, MeterProvider, and LoggerProvider instances before agent attachment, and log a diagnostic message if any are detected. [1] [2]
• Introduced a new diagnostic message ID, openTelemetryConflict, in DiagnosticMessageId for logging OpenTelemetry provider conflicts.

Unit test improvements:

• Updated agentLoader unit tests to mock and restore OpenTelemetry globals, ensuring isolation between tests and preventing side effects. [1] [2]
• Added tests for detecting and logging TracerProvider, MeterProvider, and LoggerProvider conflicts, verifying that the correct diagnostic messages are emitted when these providers are present.