plugin dev docs: migrate to plugin cutter

[ltalirz]

migrating from outdated aiida-plugin-template to more comfortable
plugin cutter.

[codecov-io]

Codecov Report

Merging #1904 into release_v0.12.2 will not change coverage.
The diff coverage is n/a.

@@               Coverage Diff                @@
##           release_v0.12.2    #1904   +/-   ##
================================================
  Coverage            54.51%   54.51%           
================================================
  Files                  246      246           
  Lines                32602    32602           
================================================
  Hits                 17772    17772           
  Misses               14830    14830

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[giovannipizzi]

Thanks!
Do you think we should remove the aiida-plugin-template repository and remove it also from the aiida-registry?

[ltalirz]

Good point - I've already added a warning on the readme of the plugin template (I'd say we keep it around for a bit longer) but I forgot to remove it from the plugin registry.
I will add the aiida-diff demo plugin there instead.