polkit: add another flag that controls how to treat the PK absent case

polkit: add another flag that controls how to treat the PK absent case

Typically if PK is not present we want to treat this as "denied". But
sometimes it makes sense to treat this case as "allowed".

In particular the combination POLKIT_ALWAYS_QUERY and
POLKIT_DEFAULT_ALLOW makes a lot of sense: it means we can enable PK
logic for actions where we so far bypassed the checks for root. With the
new combination we can have a default policy of allowing some operation
but still provide an effective hook to disable it.

Also add some debug logging about PK operations and results as they are ongoing.