cubicweb #17254139 Allow to run delete_cube() without needing the cube code / have a link between schema and cube in database [open]

Currently running delete_cube() require the cube to be installed to read its schema to generate "DROP" sql statements.

This is complex to handle because we have to drop the cube from python dependencies but it still have it installed.

I think this could be addressed by adding a relation between a Entity, Relation to the source cube in the database. Thus delete_cube() would just have to drop schema belonging to the cube.

Also having a relation between schema and cube might help developing some features.

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