Replace custom Git hook with Spotless pre-push hook

[tsaglam]

With the upcoming Spotless version 2.46.0 (see #2509), Spotless offers a Git hook out of the box (see diffplug/spotless#2553).

We could replace our own custom hook with the spotless one to streamline contributing for external developers.

The Spotless hook works on a pre-push basis (while ours is a pre-commit hook). It can be installed with spotless:install-git-pre-push-hook. It works as follows:

• Runs spotlessCheck
• If issues are found:
  • It runs spotlessApply automatically
  • Prints a message: "Spotless found problems, running apply; commit the result and re-push"
  • Aborts the push with exit code 1

[Kr0nox]

Some thoughts about that:

• We specifically decided against running apply in the pre-commit hook. I do not remember the exact reasons, but we should think about that.
• Pre push would lead to having a single spotless fix component again (which we wanted to avoid by having the pre commit hooks)
• How do we want the report viewer to be handled? Should it move back to husky or stay custom? Do we want it to also be pre-push?
• How exactly does this work? Does spottless install a githook? Where does it install it? This is important for also allowing the report viewer to have pre-commit (or other) hooks

[tsaglam]

Closed after internal discussion:

• We prefer a pre-commit hook to a pre-push hook
• Developers can still use the spotless hook if they want
• Maintainability of our hook scripts is not a big issue here