Add support for OCS API (e.g. user metadata, group folder management)

[mrustl]

Not priority for "budget" project, but in general for managing the Nextcloud instance

https://docs.nextcloud.com/server/latest/developer_manual/client_apis/OCS/ocs-api-overview.html

[mrustl]

Really needed now as we have ~ 280 users on the cloud in ~30 user groups!

And searching for users is not possible from the browser (I am lost @hsonne !)