FR: Simplify toggling ACL entries

### What are you trying to do?

I sometimes need to grant and revoke access for the same `src` to the same `dest`, and I currently have to delete/comment out the relevant ACL entry.

### How should we solve this?

Perhaps one of these would be suitable.

1. Add `action: ignore`, that switches off the ACL entry.

I've read #5108 and #6915 — I see how `action: deny` adds implementation complexity. A no-op action does not, but I'm sure there are other reasons not to do it.

2. Extend the editor interface on the website to comment/uncomment lines, or to toggle whole ACL entries.

### What is the impact of not solving this?

_No response_

### Anything else?

_No response_