[WIP] PIM-3279: Add an ajax filter

| Q                    | A
| -------------------- | ---
| Bug fix?             | Y
| New feature?         | N
| BC breaks?           | N
| CI currently passes? | ?
| Tests pass?          | Y
| Scenarios pass?      | ?
| Checkstyle issues?*  | N
| PMD issues?**        | N
| Changelog updated?   | N
| Fixed tickets        | PIM-3279
| Doc PR               | 

- [ ] Behat green on ce and ee
- [ ] Update changelog
- [ ] Check for BC
Yep, but it's related to select2. I just copied the getOption of AttributeOptionRepository