Allow user to change allowlisted fields in their own record w/o polkit auth
After the changes in #16 (closed), we should make it possible for a user to change some of the fields in their own user record without needing to polkit auth. This should make it a lot more possible for us to eventually replace Accountsservice (as decided in #1 (closed)) with direct communication w/ homed
Prior art: https://github.com/AdrianVovk/systemd/commit/082cbb1e0f78dca3210b556e985df66afd7ed8c3
Blocked on #16 (closed)