Dynamically find Grpc port

[Brandhoej]

GrpcServer per #74 now uses port 9000. However, I believe we should prioritize this port, or another one, but if it is already in use then we should select another one dynamically. For inspiration this and this, the important aspects is the general approach for finding the available port by using port 0. We also need to consider configuration for automatic deployment in an unknown environment. Given that j-Ecdar is designed as a server, we cannot always listen to a random port as the server may be configured in such a way that it relies on j-Ecdar stopping if the port is unavailable. Because of this we must also provide a way to configure j-Ecdar not to choose a random available port.