Update the display name used for this application instance.

💾 This method alters the persisted account state.

This method modifies the name of the current application's device record, as seen by other applications and in the user's account management pages.

Arguments

- `display_name` - the new name for the current device.

Notes

- Device registration is only available to applications that have been
  granted the `https:///identity.mozilla.com/apps/oldsync` scope.