daemon: support running without PolicyKit

Make the dependency on PolicyKit optional. In that case, don't
allow all methods and property access and fall back on the
standard D-Bus policies. NB: These are designed to work with
PolicyKit so most likely are not suitable at all. This is
designed for a special use case not intended for general use.

Since PolicyKit is the normal mode of operation, this feature
requires explicit opt-in, via the new `require-polkit` configure
option.
4 jobs for no_polkit in 5 minutes and 49 seconds (queued for 3 seconds)
latest
Status Job ID Name Coverage
  Build
passed #4743601
alpine

00:01:59

passed #4743599
arch

00:03:42

passed #4743600
debian

00:05:49

passed #4743598
fedora

00:04:52

87.7%