Add automatic labeling for issues

[Caellian]

This PR:

• replaces old labeler action with a different one that works on both PRs (as the previous one) and issues.
• adds support for labeling of os related things.
• adds regex checking for issue content to automatically label issues based on keywords in (mostly) titles and body.
  • because users include configs in issues, a lot of keywords can't be checked for in the issue body as too many labels would be detected (maybe in future)

The only thing I don't like is that it re-applies labels to all issues when a new one is created. I made it pick labels very conservatively, but it could be annoying in some cases.

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[Caellian]

I tested to ensure the old labeling behavior is the same and that new one works.

[Caellian]

I wanted to move stale labeling into this as well, but the changed labeler doesn't support auto-closing stale issues.