Document feature freezing starting at the 18th

Starting with 8.7 we'll be applying a feature freeze for large/complex (or maybe all) MRs starting on the 18th. This is currently not documented anywhere.

@dzaporozhets @rspeicher @DouweM @rymai @sytses: To double check, do we want to block all features during the freeze period, or only block them based on their complexity?

I think the criteria for a merge after the 18th should be that we are confident the feature is fully ready and won't break anything, which is the case for a lot of smaller MRs that just fix some bug or implement some improvement. On the 22nd itself, nothing should be merged anymore, even small MRs, except for regression fixes if necessary.

The developer and reviewer can both make that call when assigning a milestone and the Pick into Stable label, and the release manager can make the final call when cherry-picking.

Large/Complex MRs never meet that first criteria.

With this criteria, if a large feature doesn't make it in before the 18th, that developer can still spend the 18th-21nd to work on other smaller issues that can go in, and continue on the large feature on the 23rd.

Agree with @DouweM.

I put a question about code freeze in MR https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/3698#note_4795846

mentioned in commit 4b025ba0

Status changed to closed by commit 4b025ba0

Mentioned in commit pfjason/gitlab-ce@4b025ba0