Create new architecture tables

Create tables and for the new approval rule architecture.

• Create initial v2 approval rule table.
• Create join table from v2 approval rule to groups / projects / merge requests

Consult the new archtecture 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). We may also need to consider the appropriate indexes which will need to be added. In order to reduce the size of this task, models can be added separately in Create new architecture models (#512607 - closed)