Add ability to extend the set of Git pre-commit hooks

[RandomShaper]

This is very useful for forks of Godot with custom needs.

[akien-mga]

@Faless suggested on chat to add misc/hooks/pre-commit-custom-* to .gitignore, which I think is a good idea.

In theory it shouldn't be needed as the custom hooks have to be placed in .git/hooks/ and so they don't need to be in misc/hooks/. But I personally tend to make my .git/hooks a symlink to misc/hooks so that hooks update automatically, so for my use case I'd actually want to put custom hooks in misc/hooks/.

[RandomShaper]

I'm quite a noob in what comes to Git hooks. How does Git pick additional hooks normally without modifying the list of known pre-commit hooks in the main pre-commit script?

[akien-mga]

I'm quite a noob in what comes to Git hooks. How does Git pick additional hooks normally without modifying the list of known pre-commit hooks in the main pre-commit script?

What I do is symlink the whole misc/hooks/ folder to .git/hooks/. So if a new pre-commit hook is added upstream, and included in misc/hooks/pre-commit, then I get it automatically via the symlink.

But otherwise when not using a symlink, it does require a manual update (at least with the format we use for pre-commit hooks, there are likely other ways to enable them more dynamically, e.g. #46235).

[RandomShaper]

Oh, I wasn't getting it right. It's clear now.

[akien-mga]

Thanks!

[akien-mga]

Cherry-picked for 3.6.

[akien-mga]

Cherry-picked for 3.5.1.