Templates: Create new dedicated item type

[SchoolGuy]

Linked Items

Fixes #3267

Description

This adds templates as first level objects.

Behaviour changes

Old: Templates were loosely tracked via the file system

New:

• Templates are being cached in-memory
• Built-in templates no longer clutter the file-system

Category

This is related to a:

• Bugfix
• Feature
• Packaging
• Docs
• Code Quality
• Refactoring
• Miscellaneous

Tests

• Unit-Tests were created
• System-Tests were created
• Code is already covered by Unit-Tests
• Code is already covered by System-Tests
• No tests required

[codecov]

Codecov Report

Base: 65.43% // Head: 65.45% // Increases project coverage by +0.02% 🎉

Coverage data is based on head (9edae00) compared to base (23d92f6).
Patch coverage: 0.00% of modified lines in pull request are covered.

❗ Current head 9edae00 differs from pull request most recent head 981b708. Consider uploading reports for the commit 981b708 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3295      +/-   ##
==========================================
+ Coverage   65.43%   65.45%   +0.02%     
==========================================
  Files         113      115       +2     
  Lines       15155    15164       +9     
==========================================
+ Hits         9916     9926      +10     
+ Misses       5239     5238       -1     

Impacted Files	Coverage Δ
cobbler/cobbler_collections/templates.py	0.00% <0.00%> (ø)
cobbler/items/template.py	0.00% <0.00%> (ø)
cobbler/actions/check.py	55.65% <0.00%> (-1.31%)	⬇️
cobbler/modules/managers/import_signatures.py	12.01% <0.00%> (-0.05%)	⬇️
cobbler/settings/migrations/V3_3_0.py	45.36% <0.00%> (+0.91%)	⬆️
cobbler/settings/migrations/V3_0_0.py	58.51% <0.00%> (+3.30%)	⬆️
cobbler/modules/serializers/__init__.py	63.15% <0.00%> (+5.26%)	⬆️
cobbler/settings/migrations/V3_2_1.py	91.42% <0.00%> (+5.71%)	⬆️
cobbler/module_loader.py	96.15% <0.00%> (+7.69%)	⬆️
cobbler/settings/migrations/V3_3_1.py	95.00% <0.00%> (+10.00%)	⬆️
... and 2 more

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[SchoolGuy]

I need to remind myself to

1. check if the fixed windows line ending were a correct fix or if they are required for the windows auto-installation.
2. edit the testing image in OBS to include importlib.
3. transfer the Docker image to the Cobbler OBS Account.
4. fix the configgen integration.
5. move all code to the templates.
6. decide on a system to select the templates instead of the built-in ones in favour of the user-defined ones.

[SchoolGuy]

I will now start to actively push this to enable the Cloud-Init integration in #3293 to progress. Since the attempted rebase on the weekend did show too many conflicts, I will push this branch into a backup branch and restart the development of this PR.