OGM-661

@emmanuelbernard, @DavideD, This moves the cache mapping configuration to core and makes it configurable as a global option (via a new "family contract" `KeyValueStoreGlobalContext`).

I went for the "cache storage" name as suggested, although I feel it's not quite exact. Really this is not about the storage of caches, but the mapping of entities of caches. In that light, the previous proposal "cache mapping" makes more sense to me.

For assocation (document) storage it was a bit different, because that option really is about the storage of association (documents), so the "storage" name makes sense there.

WDYT?