[Xzzz]

Summary

Adds a nullable flag_activity.who column for the user who made each flag change, and writes it on every flag change. Nothing reads it yet, and flag changes are still written to bugs_activity.

First step of 2085398 (#2796), which makes the column NOT NULL and stops writing bugs_activity. Shipped in one deploy, that broke flag changes on the pods still running the old code during the rolling deploy: they insert rows without who, which MySQL (strict mode off) stores as 0, and the foreign key rejects it. Once this is deployed, every pod writes who.

Changes

• New flag_activity.who column, nullable, with a foreign key to profiles and an index on (who, flag_when). It differs from setter_id when a request is redirected, which keeps the original setter.
• checksetup fills who = setter_id on the rows without it, on every run: the existing rows, and the ones pods on the old code insert during the deploy.
• Bugzilla::Flag writes who (the current user, or the setter when there is none) for every flag change.
• scripts/remove-non-public-data.pl keeps who in the public data dump, and the users it references.
• New t/flag-activity-who.t.

Test plan

• Redirect a needinfo to someone else as another user: the new flag_activity row has that user as who and the requester as setter_id
• checksetup on a database without who: the column, its foreign key and index are added, and the existing rows get who = setter_id
• Insert a flag_activity row without who: it's saved with who NULL, and the next checksetup fills it

References

• Bugzilla link: 2088705
• First step of 2085398

[dklawren]

LGTM r=dkl