[Feature] Add users on MacOS Platform

[martintc]

I'm submitting a

• bug fix
• feature
• documentation addition

What is the current behaviour?

Adding users is not implemented on MacOS

If the current behavior is a bug, please provide the steps to reproduce and if possible a minimal demo of the problem

What is the expected behavior?

Ability to add users to a MacOS system using comtrya

What is the motivation / use case for changing the behavior?

Feature parody with FreeBSD and Linux

Please tell us about your environment:

Version (comtrya --version): 0.8.3
Operating system: MacOS 13.1

[codecov-commenter]

Codecov Report

Base: 46.27% // Head: 45.48% // Decreases project coverage by -0.78% ⚠️

Coverage data is based on head (f3b4287) compared to base (db12cde).
Patch coverage: 1.57% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #305      +/-   ##
==========================================
- Coverage   46.27%   45.48%   -0.79%     
==========================================
  Files          79       81       +2     
  Lines        2766     2836      +70     
==========================================
+ Hits         1280     1290      +10     
- Misses       1486     1546      +60     

Impacted Files	Coverage Δ
app/src/commands/apply.rs	0.00% <0.00%> (ø)
app/src/commands/contexts.rs	0.00% <0.00%> (ø)
app/src/commands/version.rs	0.00% <0.00%> (ø)
app/src/main.rs	0.00% <0.00%> (ø)
lib/src/actions/user/providers/macos.rs	0.00% <0.00%> (ø)
lib/src/actions/user/providers/mod.rs	25.00% <0.00%> (-3.58%)	⬇️
lib/src/manifests/load.rs	0.00% <0.00%> (ø)
lib/src/contexts/mod.rs	73.75% <50.00%> (ø)
lib/src/atoms/file/copy.rs	80.35% <100.00%> (+17.85%)	⬆️

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