[feature] Add firmware upgrader websocket routes

[youhaveme9]

Is your feature request related to a problem? Please describe.
Websocket routes need to be added which is introduced in openwisp/openwisp-firmware-upgrader#320

routing.py: https://github.com/openwisp/openwisp-firmware-upgrader/pull/320/files#diff-3da0660d6f22ca1b763536a072be3c84661d58bed6eb18d9cc69eeefc945767a