Optimize project MR approvals and approval rules migration

Overview

An ERROR has been showing during migrations:

Project <full-path> MR approvals <generator object list_all at 0x7f88ecd6f9e0> string indices must be integers

which triggered me to review the existing code, optimize and update where needed.

After testing the changes on a production test wave they stopped appearing.

Tasks

• Update docs if needed (workflow, runbooks, README, migration metrics, etc.)

Acceptance Criteria

• Existing UTs pass locally