Get the policy version history

Version history of the caller's own policy, newest first, each version carrying its lifecycle status, the fields it changed relative to the previous version, its attribution (changed_by, change_reason, changed_at, each nullable: null means the store did not record it, not that nothing changed), and the full stored policy.

Only versions this workspace stored appear. A workspace running on the inherited platform default has no versions of its own and reads as an empty list, which is the honest answer to "what have we changed".