Ensure document stays consistent with y.js state file

[juliusknorr]

Contributes to #5476

• fix: Clean up logic to return document state file or file content
• fix: Set base version etag to a unique id per document creation
• fix: Only cleanup earlier steps that haven't been persisted yet to the state file
• fix: Keep document table entry and only cleanup when we force it

[juliusknorr]

This might be another cause of #5420 and is not needed as we only want to load from the file content on the initial session creation

[juliusknorr]

This should still be fine as a cleanup as all steps in the saved version are also persisted in the y.js state, right @max-nextcloud ?

[mejo-]

I actually changed the logic of resetDocument() in #5481 to always delete all session data: document, sessions and steps from database as well as yjs document state file. And that will happen in the following scenarios:

• A document gets changed from outside text and there's no unsaved steps
• Cleanup background job runs for a stale document session (and no unsaved steps)
• occ command text:reset is run

I wonder whether the second case should just remove sessions and steps instead.

[juliusknorr]

Need to check the failing test:

1. The session Api
   race conditions
   sends initial content if other session is alive but did not push any steps:

I feel we might want to adjust that to account for the changed behaviour.

[mejo-]

Need to check the failing test:

    The session Api
    race conditions
    sends initial content if other session is alive but did not push any steps:

I feel we might want to adjust that to account for the changed behaviour.

I changed the cypress test to expect empty file content on /create requests if there's already a document session.

I also did some manual testing with removing the session connections (from oc_text_sessions) while having the document open.