feat: support GRPC metadata

[anthony-swirldslabs]

Description:
Adding support for passing GRPC metadata from a PBJ GRPC Client to a service and accessing the metadata in a PBJ GRPC Service implementation. Key changes:

• Map<String, String> ServiceInterface.RequestOptions.metadata() to hold the metadata
• ServiceInterface.* service methods have overridden versions with the additional RequestOptions argument added. Their default implementations delegate to the versions of the methods w/o the RequestOptions argument. While the latter legacy methods also have default implementations that throw UnsupportedOperationException. This way, the interface change is backward-compatible and existing services don't need to change, until/unless they want to start accessing the metadata.
• Client stub uses its instance RequestOptions object, and also supports the newly introduced overridden versions that accept per-request RequestOptions objects. So the client is free to either create new stubs for new metadata, or simply pass a new RequestOptions instance to a service call method.
• A new integration test is added to demonstrate and verify the behavior.

Excerpts from the generated GreeterInterface.java for the unary method (streaming methods have similar changes):

public interface GreeterInterface extends ServiceInterface {
    /** sayHello */
    @NonNull
    default HelloReply sayHello(@NonNull final HelloRequest request, @NonNull final RequestOptions requestOptions) {
        return sayHello(request);
    }
    
    /** sayHello */
    @NonNull
    default HelloReply sayHello(@NonNull final HelloRequest request) {
        throw new UnsupportedOperationException("unimplemented");
    }

    public class GreeterClient implements GreeterInterface {
        private final RequestOptions requestOptions;

        @Override
        @NonNull
        public HelloReply sayHello(@NonNull final HelloRequest request) {
            return sayHello(request, this.requestOptions);
        }
        
        @Override
        @NonNull
        public HelloReply sayHello(@NonNull final HelloRequest request, @NonNull final RequestOptions requestOptions) {
            // ...
        }
    }
}

See the new integration test for usage example.

Related issue(s):

Fixes #765

Notes for reviewer:

Checklist

• Documented (Code comments, README, etc.)
• Tested (unit, integration, etc.)

[github-actions]

JUnit Test Report

   78 files  ±0     78 suites  ±0   4m 27s ⏱️ + 1m 39s
1 352 tests ±0  1 348 ✅ ±0   4 💤 ±0  0 ❌ ±0 
7 234 runs  ±0  7 214 ✅ ±0  20 💤 ±0  0 ❌ ±0 

Results for commit 6baabdd. ± Comparison against base commit 5152c9d.

[github-actions]

Integration Test Report

    419 files  +1      419 suites  +1   18m 7s ⏱️ + 2m 26s
114 982 tests +5  114 982 ✅ +5  0 💤 ±0  0 ❌ ±0 
115 224 runs  +5  115 224 ✅ +5  0 💤 ±0  0 ❌ ±0 

Results for commit 6baabdd. ± Comparison against base commit 5152c9d.

[jsync-swirlds]

Thank you for completing this quickly.