Add the API to the capability manager

[oparoz]

Use the new capability manager available in 8.2+:
owncloud/core#15093

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@oparoz 8.2.1?

[oparoz]

It's true that with the API in beta, we could wait for it to be production ready before adding it to the capabilities. I don't think there is anything else to add to the manager.

[oparoz]

This issue was moved to nextcloud/gallery#92