✨NEW: Make aiida-project extendable for plugin packages

[mbercx]

It might be useful if the aiida-project manager was extendable so it could provide support for specific plugins. I was mainly thinking about aiida-quantumespresso. Here I often find myself having to set up a lot of different codes that are all very similar, save for the executable. Would be nice to be able to do e.g.:

aiida-project plugin qe install codes --binary-path /home/mbercx/src/qe-7.2/bin