CERN Repositories should not be hard-coded

[michi42]

The fix for #4 also allows to identify model pack repositories by URI. Therefore, there is no longer a need to hard-code the CERN GitLab repos in this service.

Instead, the initial list of enabled and disabled repositories could be passed e.g. by a system property or provided by an external package (e.g. jmad-modelpacks-cern)

[kaifox]

Definitely!
The property value could be a uri itself to a json/yaml whatever... something like
-Djmad.modelpack.initial.repo.list=https://some/file/somewhere.yaml
... then it should be easy to maintain (can sit on some git itself).

and the file could then contain

• A list of repos
• and for each one an enabled/disabled flag