PIM-2860 : add a context param in pim_enrich_categorytree_children

Add context and normalize the precedent approach introduced with https://github.com/akeneo/pim-community-dev/commit/e419cb78ab55dac1899645807c4042052d2334de

| Q                    | A
| -------------------- | ---
| Bug fix?             | N
| New feature?         | Y (extensibility point)
| BC breaks?           | N
| CI currently passes? | Y
| Tests pass?          | Y
| Scenarios pass?      | Y
| Checkstyle issues?   | N
| Changelog updated?   | N
| Fixed tickets        |
| Doc PR               |