Replace mklint with djlint

[matmair]

This PR:

• removes markuplint
• removes the HTLM checker step
• adds djlint to pre-commit
• fixes the django templates to follow a clean code style; especially:
  • Endblocks should have a name
  • images should have names
  • cleans unneeded empty lines
  • fixes white spacing around variables

Fixes #4730

[SchrodingersGat]

This is a huge improvement :)

[matmair]

@SchrodingersGat ready for merge; you will have to change the protection rules to remove the HTML check from the required checks as that no longer exists.

[SchrodingersGat]

THanks for the improvements @matmair