udevadm: emit deprecation notice in udevadm hwdb

udevadm: emit deprecation notice in udevadm hwdb

This tool was "deprecated" back in 65eb4378c3e1de25383d8cd606909e64c71edc80,
but only by removing documentation. This is somewhat surprising, but udevadm
hwdb --update and systemd-hwdb update generate different databases. udevadm
runs in compat mode and (as far as I have been able to figure out from a quick
look), it omits filename information and does some other changes to the
datastructures. The consuming code (udev) is the same in both cases, so this
"compatibility mode" seems very strange. But I don't think it's worth trying to
figure out why things were done this way. Let's just push people towards the
new code.

Inspired by https://github.com/systemd/systemd/issues/25698#issuecomment-1346298094.