feat(nextcloud): add notify_push support with test

[wrenix]

Description of the change

Benefits

Possible drawbacks

Applicable issues

• fixes #581

Additional information

Checklist

• [x] I have read the CONTRIBUTING.md doc.
• [x] DCO has been signed off on the commit.
• [x] Chart version bumped in Chart.yaml according to semver.
• [x] (optional) Parameters are documented in the README.md