feat(catalog): implement undrop & permanent delete for tabulars

[twuebi]

With #310, we're adding a cleanup task which will delete soft-deleted tabulars after a while. The idea behind that is to be able to undrop a dropped table if the deletion was not intentional.

We should add an endpoint which supports undropping a table.

It needs to:

• cancel any scheduled, i.e. not yet running cleanup task (depends on feat(tasks): cancel pending task #350)
• unset deleted_at & delete_kind in the tabular table