Better handling of flavours transitions

CMS tooling to handling transition of flavours in a given recipe is not sufficient.

For instance with https://farm.openzim.org/recipes/wikiquote_tr/history?compare=74060960-c97e-4787-baef-c9b33639644c...83acfae3-cdfc-4ff6-a9fd-25a735dab41e the wikiquote_tr recipe changed from producing mini + maxi flavours to producing only the empty (soon full) flavour.

When this recipe runs again, the CMS receives a new book without a flavour not yet declared on the CMS title. The CMS editor hence has to acknowledge that this is an expected new flavour. This is OK.

The problem is that the CMS editor would like to say at the same moment that mini and maxi flavours should not be published anymore. This is not possible. It is possible to fully delete these flavours (which in turns delete the book) but I don't feel like this is what we wanna do. We should probably rather remove mini and maxi from the catalog(s) but keep files on the FS (to keep ongoing downloads working fine, and to keep a previous version as usual), and then once we have two books with the target flavours we can delete the old ones.

This process is maybe to complex to fully automate, but if we agree this is what we wanna do we can discuss potential implementation (maybe simply being able to hide a flavour from the catalog is sufficient and the rest can be handled by humans clicks).

Start by tracing how the CMS handles a recipe run that introduces a new flavour and how flavour visibility in catalogs is represented. Review the relevant CMS entry points for catalog publication and filesystem retention; done should allow old flavours to be hidden from catalogs while keeping their files available until the replacement flavours are established.