Mediator should be able to start python engines

[thrau]

Currently the python engines start the server socket and engines using a main.py, which takes a --host and --port argument to bind the server socket.

We need some way of starting a python engine from the mediator in go.

This will require:

• [x] Creating a special type of EngineRuntime, or a special PluginEngine wrapper. Or some completely other way.
• [x] A way to actually hold the python process
• [x] A communication channel between the python engine and the mediator (e.g., via some line-based protocol commands. for example the python engine returns "running " when the server socket is up with the port it's listening to)
• [x] A way to list the available python engines
• [x] A way to integrate the engines into the engines build cycle

[thrau]

last point became obsolete by allowing users to specify multiple plugin directories when starting the mediator

for example:

make dist
dist/mediator -plugins dist/engines/ -plugins engines/engines-py

obviously you need to prepare the individual engines in engines-py first by creating a .venv directory and installing the necessary requirements.