Export/Import user (aka "migrate")

[hughrun]

Preliminary work on an Export/Import flow for users

This is very preliminary and subject to change, potentially in major ways.

Intended to resolve #1012

Users can export a JSON file and import the file into another instance.
Uses serializers.serialize so this is just a straight Django dump, not an ActivityPub JSON format.

• import user profile
• import selected user settings
• import goals
• import books (as combined Book and Edition objects) and their authors
• import shelves and ShelfBooks
• import lists and ListItems
• import reviews (as combined Review and Status objects)
• import readthroughs
• saved lists
• follows
• user blocks
• load book images
• flip curation on group-curating lists (see below)
• use task manager for imports

Related future work

We will also need a way to indicate in the old instance that the user has moved. I am anticipating we'll do that in a separate PR, using a Move ActivityPub action similar to how Mastodon does it ("Alice has Moved Alice to Bob") but also possibly Moveing book lists.

Exclusions

• I initially did not intend to migrate quotes and comments but we could do this fairly easily.
• as Groups are not currently ActivityPub-aware objects, I have excluded them, though in future these need to be ActivityPub objects and therefore included. Not this also means we should flip any Group curated lists back to default. i.e. Groups can only exist between users who are all local users.

[hughrun]

Work for this is happening at https://codeberg.org/GuildAlpha/bookwyrm for now and will come back here eventually.

[mouse-reeve]

thank you SO much for working on this and feel free to ping me here or on mastodon if I can answer any questions

[skobkin]

By the way, @mouse-reeve, does bookwyrm support move activity right now? If not, it'd be good to have it with migration to be able to automatically move followers to the new instance.

[hughrun]

@skobkin Not yet. My plan is to do this in 2 steps: first just enable user export/import, then add Move as a separate PR immediately following - for user ids and potentially lists. The second should be fairly straightforward once we sort out export and import, though I guess technically they don't rely on each other.

[skobkin]

@hughrun Sounds awesome.

Sorry if it wasn't clear, but I didn't mean that it should be implemented in this PR.

[hughrun]

closing this in favour of #2980