Allow for Draft PRs to not lock state

[kneemaa]

#1007 brought back plans in draft PRs. Only downside is that plans in a draft PR lock the project so that a Open PR cannot plan.

Requested Solution

An option to enable/disable locking projects in a Draft PR.

Reasoning

Draft PRs can iterate quickly and having them reserve the lock prevents Open PRs from progressing

When working in a commonly updated directory, a draft PR is a great way to discuss changes before opening a PR. But when a Draft PR has the project/directory locked, Open PRs cannot progress.

[lkysow]

Note that if draft pr plans are enabled users can apply from those PRs too. So if you disabled locking you'd also want to disable applies.

[kneemaa]

@lkysow that's a good point, disabling applies would be good as well.

[ghostsquad]

yes please

[dupuy26]

If your repo configuration has apply_requirements including "mergable" then applies would automatically be disabled for a draft PR (since draft PRs cannot be merged).

If there is a feature for managing draft PRs and locks, it would also be useful to have locks released when a PR changes from 'draft:false' to 'draft:true'.

[scallisterdd]

When apply_requirements include mergeable, it may also make sense to release existing locks once a PR is no longer mergeable as well.