lint: Check for potential uid drift for files in `/etc`

[cgwalters]

Now that we have parsers for both tmpfiles.d and sysusers.d, we can detect the case where files in /etc are owned by a floating uid/gid and warn.

However we should not warn if there's a tmpfiles.d entry which does a chown, which is a standard workaround for components/packages which have floating uid/gids; e.g. we shouldn't warn on if we detect
/usr/lib/tmpfiles.d/polkit.conf:Z /etc/polkit-1/localauthority - polkitd polkitd

(Humm actually this is tangential but it seems that rpm-ostree auto-synthesized

cat /usr/lib/tmpfiles.d/polkit-tmpfiles.conf 
d /etc/polkit-1/rules.d 0750 root polkitd - -

which seems kind of wrong because it should actually be Z here probably)

[rishi-jat]

@cgwalters can I work on this issue ?

[cgwalters]

Sure; this is a slightly nontrivial one but happy to help mentor.