[WIP] PIM-3095: Cascade delete on associations on MongoDB impl

| Q                    | A
| -------------------- | ---
| Bug fix?             | Y
| New feature?         | N
| BC breaks?           | N
| CI currently passes? | N
| Tests pass?          | ?
| Scenarios pass?      | ?
| Checkstyle issues?*  | ?
| PMD issues?**        | ?
| Changelog updated?   | ?
| Fixed tickets        | PIM-3095
| Doc PR               |