[CLI] Simplify default create-user script

[LoicPoullain]

Issue

The default create-user script generated by createapp has a lot of commented code that can be "intimidating" and is eventually not very useful. This PR removes the commented lines about groups and permissions and moves them to the documentation.

Solution and steps

• Update the template
• Update the groups & permissions page.

Checklist

• Add/update/check docs (code comments and docs/ folder).
• Add/update/check tests.
• Update/check the cli generators.

[codecov-commenter]

Codecov Report

Merging #927 (b5a0b68) into v2-4-0 (fe59733) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           v2-4-0     #927   +/-   ##
=======================================
  Coverage   98.93%   98.93%           
=======================================
  Files          86       86           
  Lines        1694     1694           
  Branches      406      406           
=======================================
  Hits         1676     1676           
  Misses         18       18           

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