Unable to configure nextcloud account

Description

https://forum.turris.cz/t/nextcloud-on-tos5-2-1/15543

When user tries to configure new nextcloud account nothing is actually configured.

Validation error could be found in /var/log/lighttpd/error.log:

jsonschema.exceptions.ValidationError: {'module': 'storage', 'kind': 'request', 'action': 'configure_nextcloud', 'data': {'c
     redentials': {'login': 'nextcloud', 'password': 'superSecretPassword'}}} is not valid under any of the given schemas

Culprit is in the outdated call to backend, which tries to use storage module instead of nextcloud module.

How to reproduce

Install Nextcloud, set external storage and try to configure Nextcloud in Foris Storage tab.

Reproducible on TOS 5.2.1 to 5.3.0 on Turris 1.x and Mox. Probably also on all Turris routers, because it doesn't seem to be related to specific HW.

Expected behavior

Nextcloud will be configured after a while and there will be message saying that nextcloud is configured and ready.

Actual behavior

Spinner with "configuring nextcloud" message spins forever and after reload of page, the same form is shown, prompting user to configure nextcloud account.

Also there is a stacktrace of foris-controller validation in lighttpd's error.log