Complete Migrations of Bookwyrm Accounts across instances

[CSDUMMI]

This PR aims to implement #1012. It introduces new export and import functionality, that allows users to export their entire account and all associated media in a self-contained tar file.

Archive structure

The tar.gz archive contains three parts:

1. archive.json: Containing the user settings, names and books used by the user.
2. avatar.png/avatar.jpg: A user's avatar image if present
3. covers/: the book covers used by the user

Implementation

This project was implemented in collaboration during the first Guild Alpha Sprint.

We decided to use a custom JSON archive as the basis of this proposal, as @hughrun had already done work on that, which we used as a base.

On this we added:

• Improved serialization of the archive.json
• Move exporting and importing to celery tasks
• Wrap the archive.json into a tar archive
• Add media files to the archive
• Unit Tests of the import and export process

Due to time constraints we couldn't implement everything needed. Here are the tasks, that we know of, that still need work:

• Cool-down period between creating archives to prevent overloading the server
• Regularly scheduled task to remove old archives according to an environment variable
• Notification on import & export completion
• Error handling & retry mechanism. Currently when an import or export fails the Task status remains active. The status doesn't show "failed" and no error is given.
• Admin controls

Hopefully with our work as a base, the remainder can be undertaken by BookWyrm itself to bring this PR to completion.

Screenshots

Known Bugs

test_export_user.py Errors

• ExportUserViews.test_download_export_user_file is throwing: bookwyrm.models.bookwyrm_export_job.BookwyrmExportJob.DoesNotExist: BookwyrmExportJob matching query does not exist.
• ExportUserViews.test_export_user_get is throwing: Exception: line 367 column 5 - Warning: inserting implicit <p>

Contributors:

• @CSDUMMI
• @dannymate
• @hughrun
• @Tomat0

Special thanks to @Ryuno-Ki and @circlebuilder

[hughrun]

@CSDUMMI we need to fix a couple of things before pulling this into main. Can you please change the target branch to user-migration? We can then deal with any merge conflicts, pull it across, and will have a branch to work with on the main bookwyrm repository instead of trying to run through your repo.

[CSDUMMI]

I've changed the base branch now.

I'm available to answer any further questions on this here.