👌 IMPROVE: Allow aiida-project destroy to only remove environment

[mbercx]

Often in a development project, I want to nuke the Python environment so I can rebuild it from scratch without losing anything else from the the project. One way would be to have an option to only destroy the environment, e.g.

aiida-project destroy --env

Or --environment, since destroy command should be used with care anyways. Alternatively, we can also have aiida-project create complain if the environment already exists, but prompt to have it overridden.