Backend: Add API endpoint to publish a components repository in the catalog

Problem

As owner of a project containing components, I want to be able to set my project as catalog resource so that my components repository is listed in the private catalog under the project's root namespace.

As an extension of Backend: Create a service to convert project to... (#387064 - closed) we need an API endpoint to add a project as a catalog resource.

Proposal

After we decide on which level we want to implement CI Catalog, this might be an API endpoint implemented on a group or instance level.