Placement scriptlet not called when moving instances between projects

[victoitor]

When moving an instance between projects and a placement scriptlet is defined through instances.placement.scriptlet, it is not called to place the instance in the new project. This can lead to inconsistent configurations similar to #589 if the consistency of a configuration is checked through the placement scriptlet and user keys instead of through incus defined keys.

[victoitor]

Btw, I know that consistency cannot be enforced everywhere. But it seems projects are designed to have different rules for consistency and moving between them should at least recheck those rules at least once. So it would make sense to call the placement scriptlet as if enforces general rules.