Unban everyone who does not have a matching policy automatically

[Gnuxie]

Context: https://matrix.to/#/%21IaWNErZAgQUhGqJXjX%3Amatrix.org/%24AhrzeZSiGacU8ZHi8c7P426nJPcRtt9jfzlljRI9-HI?via=matrix.org&via=envs.net&via=kde.org

To make this happen we need to provide new users a migration path to put all their room bans into a list.
And then let them enable the thing to unban them.