add rollback functionality for a pull

Problem/Motivation

It would be useful to be able to roll back an import when something has gone wrong.

We can't use DB transactions, because our use of batch API means that entity saves are in different PHP requests.

However, we could add the revision ID to the import status entity, and then roll back based on that. Obviously, this requires entity types to support revisions, and to have revisions enabled.

I'm adding a concept of a pull set ID as part of 🐛 pulled dependencies don't participate in the batch, risk of PHP execution timeouts Active , so that could be used to identify which entities to roll back.

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes