Users have asked for this multiple times since last release.
Not sure on the best default value, but I'm going with the
stable/classic one, at least for the initial release to avoid needing
migrations.
In the future we may reconsider this for new users.
Though the code appears slightly different, it should be semantically
equivalent. APIUser equality is implemented on `Id` and `Host` should
never transition from non-null to null.