🔧 MAINTAIN: Move pylint plugin to external package

[chrisjsewell]

This will allow pylint/pre-commit to be called from anywhere,
and also allows for plugins to use it if necessary.

[chrisjsewell]

I guess this seems a good a place as any to house it @sphuber?

As mentioned in #5182, there is probably some improvements that can be made with this plugin, but I think it's already better than having to add a tonne of pylint disables, for uses of e.g. Entity.objects.
Naturally, if there are any replies to pylint-dev/pylint#1694 (comment), then I will update it.

[chrisjsewell]

The other approach would be to turn it into a standalone package. I can do that but probably not today

[codecov]

Codecov Report

Merging #5190 (b470559) into develop (78c7b72) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff            @@
##           develop    #5190   +/-   ##
========================================
  Coverage    81.00%   81.00%           
========================================
  Files          535      535           
  Lines        37402    37402           
========================================
  Hits         30293    30293           
  Misses        7109     7109           

Flag	Coverage Δ
django	75.82% <ø> (ø)
sqlalchemy	74.92% <ø> (+0.01%)	⬆️

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[sphuber]

The other approach would be to turn it into a standalone package. I can do that but probably not today

That's what I was going to suggest. No need to do it today

[chrisjsewell]

Ok moved it to https://github.com/aiidateam/pylint-aiida