Support For Granular Locking Mechanisms.

### Details

First of all, we really thank you for this project. It's really one of my favorite GHA related projects.

## The Problem
We recently realized that sticky locks lock on a user level, not on a PR level.
This recently caused a problem for us because one of our developers forgot to merge and deployed another PR, effectively rolling back the changes of his previous PR.

## The Suggestion
We would like it if locks could also work on a PR or Branch basis.

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I would be glad to contribute if that's ok, but I wanted to check if my assumption and suggestion was valid first.