Fix/mongo direct writer images

 - media are now embedded inside documents, so work similar to Metric and Price
 - direct writer can now work with media as they are part of the product document

| Q                    | A
| -------------------- | ---
| Bug fix?             | Yes
| New feature?         | No
| BC breaks?           | Yes
| CI currently passes? | Yes
| Tests pass?          | Yes
| Scenarios pass?      | WIP
| Checkstyle issues?*  | No
| PMD issues?**        | No
| Changelog updated?   | Yes
| Fixed tickets        | N.A.
| Doc PR               | N.A.