Goal: 
We export information about custom repositories now within the blueprint file. Later we provide the option to import a blueprint alongside with Custom repositories: if the user does not have the given custom repositories that are listed in the imported file, we try to create those repositories in another service - Content on the user's behalf. In case something goes wrong, such as users already having that Repo with different specifications, we notify users about that and keep the repo as is.

We should test this behaviour.

https://github.com/osbuild/image-builder/pull/1381/

https://github.com/osbuild/image-builder-frontend/pull/2626