Create new architecture models

Create models for the tables added in Create new architecture tables (#512606 - closed).

• v2 approval rule model
• v2 approval rule to groups / projects / merge requests model

Consult the new archtecture in the Architecture Design Document and the models 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).