Pim 2712

| Q                    | A
| -------------------- | ---
| Bug fix?             | No
| New feature?         | No
| BC breaks?           | No
| CI currently passes? | 
| Tests pass?          | Yes
| Scenarios pass?      | Yes
| Checkstyle issues?   | No
| Changelog updated?   | Yes
| Fixed tickets        | PIM-2712
| Doc PR               | 
This class is used on (post|pre)Flush and can only get the smartRegistryManager. So I cannot inject the channelManager from DI.

The method is public because it's used by the indexCreator made by @BitOne (this method was actually in the indexCreator)