[TEST] Functional tests for OTLP GRPC MTLS export

[marcalff]

This is a follow up on:

• [EXPORTER] OTLP GRPC mTLS support #2120

Add functional tests for validating OTLP gRPC with client certificate chain + Server ca certificate.
Ref- https://github.com/open-telemetry/opentelemetry-cpp/tree/main/functional/otlp

[github-actions]

This issue was marked as stale due to lack of activity.

[github-actions]

This issue was marked as stale due to lack of activity.