`ProjectItemPositionManager` needs to be refactored to support `WebhookAutomationRule`

[humitos]

It fails because we are using polymorphic models here. It checks for the maximum priority on the actual model, but there is no objects there, so it starts from 0 again, but there is another model --using the same db table-- with priority=0 already, so it fails. We need to filter by all polymorphic models to fix this.

I didn't want to deal with that just now, so I skipped this positioning for now since we will create the objects manually from the Django shell for now.

The code is at https://github.com/readthedocs/readthedocs.org/blob/main/readthedocs/projects/ordering.py#L6

[stsewd]

Another way would be to stop using the polymorphic modeling, and use the existing model instead. We would need to add an extra field to track the type of match done (file patterns or regex).

[humitos]

Yeah, removing polymorphic is probably the right path. I didn't want to start there because that will be a big refactor that's out of the scope of the feature I was building.

However, if we will consider that refactor, I would probably propose directly to re-think automation rules as a whole and consider a new modeling that matches what I described in #12788