Block pull requests as long as changes are requested

[yardenshoham]

We add a new lgtm/blocked state that makes sure no pull request gets merged while it still has changes requested.

• Block merge on negative review #73

[silverwind]

I find it sometimes helpful to merge even with a block in place. Have observed that sometimes maintainers forget to clear a block, holding up a merge.

[yardenshoham]

I'm trying to think how to avoid what happened in go-gitea/gitea#22664, it blocked the queue and was not ready for merge

[silverwind]

Don't think it can really be automated. We could block merge by regular mergers, and admins could merge even with the lgtm bot failing (because of the block).

[yardenshoham]

I understand, maybe we should sync a few PRs in the merge queue, not only the earliest one

[silverwind]

Wouldn't have closed this yet. If admins want the merge block reflected in LGTM bot and are willing to forcibly merge long-blocked PRs that are ready, we could do it.

Otherwise, I guess current situation is fine. A merger should just check the blocks, ask for unblock, and if there's no response within a few days, merge.