Lock users while exporting/importing

[IljaN]

During an export, the user's storage and metadata must be locked to prevent changes happening during the export and avoid inconsistent states.

One idea is to have a command to lock then unlock the user, using the new permanent locks: owncloud/core#31651. Limited to master / OC 11 currently.

Another one would be to lock the user when running occ export:xxx, this would require a single export command because locking/unlocking for each metadata type will likely result in inconsitencies.

@jvillafanez @IljaN

[PVince81]

I think this is a must have to avoid data loss in case of concurrency during export.

Any estimate ?

[IljaN]

Effort based on assumption that disabling the user during export/import works for us.

[PVince81]

What also comes to mind: we should also be able to export disabled users and keep them disabled. This could happen for accounts temporarily disabled by the admin or accounts that are kept for a longer time because they contain important data to recover later on (ex: transfer ownership)