rec: Add custom tags to RPZ hits

rec: Add custom tags to RPZ hits

This commit adds the possibility to set custom tags to a RPZ zone,
adding these tags to the policy ones (that can be set with Lua)
when a policy matches.
It does so by creating a new PolicyZoneData object that is shared
between the zone and all the policies that it holds, in order to
- avoid duplicating the name, priority and tags for each policy ;
- prevent a circular dependency between shared pointers for the zone
and its policies.

It also refactors the handling of RPZ policy hits in `startDoResolve()`
to remove some code duplication.