feat(cmd-api-server): add gRPC plugin auto-registration support

[petermetz]

1. The API server supports gRPC endpoints, but plugins are not yet able
   to register their own gRPC services to be exposed the same way that was
   already possible for HTTP endpoints to be registered dynamically. This
   was due to an oversight when the original contribution was made by Peter
   (who was the person making the oversight - good job Peter)
2. The functionality works largely the same as it does for the HTTP
   endpoints but it does so for gRPC services (which is the equivalent of
   endpoints in gRPC terminology, so service === endpoint in this context.)
3. There are new methods added to the public API surface of the API server
   package which can be used to construct gRPC credential and server objects
   using the instance of the library that is used by the API server.
   This is necessary because the validation logic built into grpc-js fails
   for these mentioned objects if the creds or the server was constructed
   with a different instance of the library than the one used by the API
   server.
4. Different instance in this context means just that the exact same
   version of the library was imported from a different path for example
   there could be the node_modules directory of the besu connector and also
   the node_modules directory of the API server.
5. Because of the problem outlined above, the only way we can have functioning
   test cases is if the API server exposes its own instance of grpc-js.

Signed-off-by: Peter Somogyvari peter.somogyvari@accenture.com

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A Must Read for Beginners
For rebasing and squashing, here's a must read guide for beginners.