Simplify external gRPC API access

[mbfm]

It should be simpler for users to interact with CARL's gRPC API. Currently, this involves relatively many dependencies: https://opendut.eclipse.dev/book/development/carl-grpc-api.html

Tasks:

• [ ] Offer gRPC Reflection. This allows interacting with the gRPC service without having the Protobuf files downloaded.
• [ ] ~~Offer an endpoint for downloading the CA certificate. This allows connecting over TLS by simply knowing the server address. This endpoint should be reachable without TLS nor authorization.~~ → This would be vulnerable to MitM-attacks. We could still offer a download after authentication, e.g. in LEA.