perf: Use generator/count query on cleanup tasks

[juliushaertl]

Fix https://github.com/nextcloud/text/issues/5904

• [x] Avoid running out of memory when iterating over documents
• [ ] Think about a way to do the document cleanup later on as iterating over all documents and deleting the y.js state files is not feasible on larger instances
  • [x] Implemented this now for testing, in general this approach should work fine as we do set this value also for new file creation if no steps were pushed.
  • [ ] Would still need some testing and thinking if the reset on create could again cause problems

[mejo-]

Replaced by https://github.com/nextcloud/text/pull/5918