Any plan to support customize the otlp gRPC header for authentication？

[aaron-ai]

Actually, opentelemetry-java allows user to customize the metadata in the header, which is convenient to implement our own authentication in collector, any plan for cpp? Thank you.

Is your feature request related to a problem?
No.

Describe the solution you'd like
Provide the ability to customize the gRPC header.

Describe alternatives you've considered
No.

Additional context
Nothing.

[lalitb]

This is an important requirement to allow custom metadata headers for authentication. Though as of now, it's not planned for the 1.0.0 release, unless someone wants to contribute the support - due to limited available bandwidth with us.