stats/opentelemetry: Introduce Tracing API

[aranjans]

Overview

This pull request implements the OpenTelemetry tracing support in the gRPC-Go library as outlined in proposal A72. The implementation provides a robust framework for tracing gRPC calls using OpenTelemetry, facilitating a smooth migration path from OpenCensus tracing.

Key Features

• OpenTelemetry Tracing API: Introduces a new API for enabling and configuring OpenTelemetry tracing within gRPC. This includes the addition of TraceOptions in the Options struct to allow users to specify their TraceProvider.

• Context Propagation: Implements context propagation between gRPC clients and servers using OpenTelemetry's TextMapPropagator. This ensures that trace context is correctly passed along with RPC calls.

• Migration Path: Provides a clear migration path from OpenCensus to OpenTelemetry, allowing users to transition their tracing implementations without breaking existing functionality. This includes support for both cross-process and in-binary migration scenarios(this will be added in separate PR).

• Tracing Information: Captures detailed tracing information during the RPC lifecycle, including events for outbound and inbound messages, retries, and load balancer delays. This information is essential for monitoring and debugging distributed systems.

RELEASE NOTES:

• stats/opentelemetry: Added OpenTelemetry tracing support in gRPC-Go, enabling enhanced observability and a migration path from OpenCensus.