Account provisioning for large user directories

Is your feature request related to a problem? Please describe.

The ProvisionAccounts repair step runs on occ maintenance:repair or occ upgrade.

This means we use IUserManager.callForAllUsers to loop over all users and check for each if there's a matching provisioning configuration.

• IUserManager.callForAllUsers is, with large user directories, slow.
• While running the provisioning we don't have access to the user's password, unless a master password is used, and therefore it's not necessary to create the account upfront because we cannot run a sync/quota/training job.
• OCA\Mail\Service\Provisioning\Manager uses MailAccountMapper to create/update/delete a mail account, but the background jobs are never scheduled somewhere? For non-provisioned account's that's done in AccountService.save. However, there's a repair step to add the background jobs when missing.

Start with lib/Migration/ProvisionAccounts.php and trace the occ maintenance:repair and upgrade paths using IUserManager.callForAllUsers. Then inspect OCA\Mail\Service\Provisioning\Manager, MailAccountMapper, and AccountService.save, focusing on account creation and background-job scheduling. Done means the provisioning behavior addresses large directories and the stated job-scheduling gap without relying on unavailable user passwords.