Install drop-in to order early boot services after run-lock.mount

An out-of-tree patch was added some time ago that made /run/lock/ a tmpfs by changing the systemd code. This is now being dropped in favour of a standard early boot mount unit. Ensure lvm2 units that run before sysinit.target are ordered after this new unit, if it exists, so that the content is not overshadowed by a new tmpfs while they are already running.

Closes: #1071175