Expose service documentation

[slinkydeveloper]

Could we expose the service documentation when listing the services in meta?

[slinkydeveloper]

Look at https://github.com/protocolbuffers/protobuf/blob/main/src/google/protobuf/descriptor.proto#L990

[slinkydeveloper]

Can be problematic: https://github.com/protocolbuffers/protobuf/issues/8728

[slinkydeveloper]

This is still relevant with the new interface refactor. In Java we could extract the javadocs and use those as documentation.

[slinkydeveloper]

Starting point for Java is this one: https://docs.oracle.com/en/java/javase/11/docs/api/java.compiler/javax/lang/model/util/Elements.html#getDocComment(javax.lang.model.element.Element)