Add new v2 approval rule associations to user and user group for new approval rule architecture

Add new v2 approval rule associations to user and user group for new approval rule architecture. Update the associations for v2 approval rules accordingly.

These tables store which users and groups can approve merge requests. Both tables will need to have a defined sharding key similar to !179861 (merged).

For reference consult the new architecture in the Architecture Design Document and the tables which were created in Draft: [ci skip][DO NOT MERGE][PoC] Start of Po... (!171114 - closed) and Draft: [ci skip][DO NOT MERGE][PoC] Integrate v... (!174517).