Split ega.yml into several ones: one per LocalEGA instance

[silverdaz]

It would be nice to have the docker containers of a given LocalEGA instance all on the same network, but on a different network than the other instances.

Moreover, we could try to create separate .yml docker-compose files: one per instance.

Our fake CentralEGA would also have its own network and its own .yml docker-compose file.

[blankdots]

Splitting into different networks is definitely possible:

• as done in these commits: https://github.com/blankdots/LocalEGA/commit/7fa18a3f7e4c3a2266257d5d19ce8005313f0d6b and c8e96ce
  Note: running them on the same host might pose problems with the bridge device on macOS as @silverdaz pointed and explained here: https://docs.docker.com/docker-for-mac/networking/#there-is-no-docker0-bridge-on-macos

Looking a bit also into https://docs.docker.com/compose/compose-file/compose-file-v2/#aliases and changing names