Detect and store repository type

We need to add an enum type on the Repository model, in order to store if it's a worker or a iiif one.

The create_repo method must fetch the .arkindex.yml content, and just check its version (2) & type values.

If either values are missing or invalid, the repository is not created (error 400).

Once created, a dataimport is started, and the frontend should display that dataimport.

Requires an update on the frontend to set corpus mandatory for IIIF repository imports only