new policy engine

This implements the more important parts of #535 and some issues linked from there. Except for declarative configuration parts; those came mainly through !1313 (merged).

added feature major labels

assigned to @vcunat

mentioned in commit b2b7d9f9

merged

I think

• we can defer further fixes and improvements to the 6.0 branch;
• we don't close relevant issues at least until we have some basic user docs and are ready for public testing.

mentioned in merge request !1410 (merged)