Add support for JWT tokens for Temporal server authorization

[Spikhalskiy]

What was changed

Added support for AuthorizationTokenSupplier to simplify providing JWT or another kind of auth tokens.
Added WorkflowServiceStubsOptions#grpcClientInterceptors that allow providing any custom grpc interceptors.
Added WorkflowServiceStubsOptions#grpcMetadataProviders that provide a handier way to provide dynamic gRPC headers.

Why?

To improve extensibility of Temporal Grpc Stubs and allow Temporal users to provide JWT tokens in an easy and clean manner.

1. Closes Add an easy way to provide JWT tokens to java-sdk for server calls #671

[Sushisource]

Overall this approach looks totally fine to me as a way to generically attach JWTs -- really it's even just any authorization header. Maybe we should call these classes authorization, and then we could have JWTTokenSupplier be an implementation of AuthorizationSupplier or something like that, which handles slapping bearer on the front of the token.

I think adding JWT into there makes sense if we have a way to supply the JWT payload & secret info so that we actually handle creating the JWT token for them, but that's substantially more work than this, so maybe something for later. Not sure how far we were looking to go here. The easiest-to-use version of this would probably be allowing the user to specify the namespaces / other info you mentioned is in the JWT payload, and their secret (or an interface to access it) and then creating & signing the JWT for them and then passing it into the code you've added here to attach to the header.

[Spikhalskiy]

@Sushisource I discussed it with @sergeybykov and the generation/construction of JWT tokens shouldn't be a part of SDKs. Tokens are usually generated and provided by separate services and SDKs should just pass them through.

[Sushisource]

Awesome, LGTM