units: add [Install] section to remote-cryptsetup.target

This makes this target the same as remote-fs.target in this regard. In practice
it probably doesn't make that much difference, because all encrypted devices
that are part of remote-fs.target (marked with _netdev) will be used for mount
points, so they will be pulled in anyway individually, but with this change any
such device will be configured, even if it is not pulled by any other unit.

(cherry picked from commit 8f462b07)
(cherry picked from commit eaaa52cc)