Detect conflict of ZIM names across recipes

[benoit74]

ZIM names must be unique to a single recipe, no matter the warehouse path / offliner in use, to avoid conflicting / overriding recipes and hard to debug situations.

Even when ZIMs are published to distinct warehouse path, I don't think that have conflicting names can bring anything good.

We need to be able to detect that issue at recipe configuration time and prevent such configuration from being saved, based on currently configured recipes. I.e. fail with something like "you cannot use this ZIM name which is already used by this recipe".

The corollary is probably that we must change / remove the ZIM name at recipe clone time, because this is the typical situation where we create a conflict, and should the editor forget to modify this setting, then we have conflict / overriding recipes.

This will not save us from a recipe overriding a ZIM which has been manually uploaded or created by a deleted recipe, but this last case is probably very rare and very hard to diagnose by the machine (and we might want to do it intentionally).