Publish App to Nextcloud App Store

https://nextcloudappstore.readthedocs.io/en/latest/developer.html#publishing-apps-on-the-app-store

Also see https://plan.tugraz.at/project/399/task/24431

• Get certificate from Nextcloud
• Create store account
• Set VPU EMailaddress in store account on https://apps.nextcloud.com/account/
• Prepare release with changelog and documentation
• Release Application on https://apps.nextcloud.com/developer/apps/new