PIM-3279: Add an ajax filter

| Q                    | A
| -------------------- | ---
| Bug fix?             | Y
| New feature?         | N
| BC breaks?           | N
| CI currently passes? | Y
| Tests pass?          | Y
| Scenarios pass?      | Y
| Checkstyle issues?*  | N
| PMD issues?**        | N
| Changelog updated?   | N
| Fixed tickets        | PIM-3279
| Doc PR               | 

- [x] Behat green on ce and ee
- [x] Update changelog
- [x] Check for BC
If i'm not mistaken, it was created specifically for the select2 ajax-loaded options - this method's signature exactly matches the interface