Allow access to ContextPropagationInterceptor outside of GrpcClientFactory

### Is your feature request related to a problem? Please describe.
as described in #1641 I have a scenario where I have to create multiple clients during runtime as I know the addresses only at run time.

I went the proposed route and manage my channels and clients myself - but doing that, I can't use `EnableCallContextPropagation`.

### Describe the solution you'd like

Would it be possible to make `ContextPropagationinterceptor` public, so we could use it in such a use case?

I could rebuild an interceptor that does something similar, but as there is already well tested code for one, I'd like to use that one.

A nice way would be to add some options for known interceptors to the CallInvoker class, or make that one configurable?

Start by reviewing GrpcClientFactory, EnableCallContextPropagation, and the ContextPropagationInterceptor mentioned in the issue. Determine how the interceptor could be exposed for clients and channels created at runtime, then verify that callers can use the existing context-propagation behavior without GrpcClientFactory.

Written by the indexing model from the issue text.