userprovider owncloudsql

[butonic]

I am currently using glauth and the graphapi app to use my owncloud10 instance as a user provider for ocis using the ldap user provider ... while that works, it adds significant lag, to a point where listing shares takes ages when a lot of user have to be fetched by claim.

So, I sat down and implemented a small owncloudsql user provider. It works ok, and way faster then my current setup.

We added a new backend for the userprovider that is backed by an owncloud 10 database. By default the user_id column is used as the reva user username and reva user opaque id. When setting join_username=true the reva user username is joined from the oc_preferences table (appid='core' AND configkey='username') instead. When setting join_ownclouduuid=true the reva user opaqueid is joined from the oc_preferences table (appid='core' AND configkey='ownclouduuid') instead. This allows more flexible migration strategies.

[update-docs]

Thanks for opening this pull request! The maintainers of this repository would appreciate it if you would create a changelog item based on your changes.

[C0rby]

Kudos for writing tests!