Let's define a clean way how we can reestablish file watches in homed.
This is a relevant in case we overmount /home/ as a whole. It's very
useful for our testcase in particular.
This ensures that a user-specific blob directory exists in
/var/cache/systemd/homed for as long as the user exists, and gets
deleted if the user gets deleted.
It also advertises this blob directory via the user record, so that
clients can find and use it.
This tries to add information about when each option was added. It goes
back to version 183.
The version info is included from a separate file to allow generating it,
which would allow more control on the formatting of the final output.
