Migrate FileUploader, etc to WorkManager

[tobiasKaminsky]

As of https://github.com/nextcloud/android/issues/10692 we need to migrate FileUploader, SynchronizeFileOperation and SynchronizeFolderOperation before we can bump sdk again.

This needs to be done before November due to Gplay restrictions.

[tobiasKaminsky]

• centralize functions to start upload within FileUploader
  • either use fileUploader intent (old) or uploadWorker (new)
• adopt from FileUploader.onStartCommand to worker
  • retry: start worker with retry-command to upload one by one
  • start new uploads: add them to db, start worker to upload one by one
• write new uploderWorker
  • one worker, which checks after start for current state of onWifi/charging
  • gather fitting uploads from UploadsStorageManager
  • upload each file one by one
• make FileUploaderBinder to work with both implementation
• uploadWorker only enabled for Android 12+ and dev version

This will then be one worker to process whole queue, which is always in UploadsStorageManager (FileUploader had an internal mPendingUploads queue, which we shall not adopt).

@AlvaroBrey for review