Raise exception for misconfigured repos in osbuild-depsolve-mpp

[Achilleas Koutsou]

When a repository is not configured properly, it can lead to the following uninformative assertion error:

osbuild/tools/osbuild-depsolve-dnf

Lines 66 to 75 in 5579257

 if "name" in desc: 
     repo.name = desc["name"] 
 if "baseurl" in desc: 
     repo.baseurl = desc["baseurl"] 
 elif "metalink" in desc: 
     repo.metalink = desc["metalink"] 
 elif "mirrorlist" in desc: 
     repo.mirrorlist = desc["mirrorlist"] 
 else: 
     assert False 

Let's make a typed exception for this and return a structured error with a message that's more useful for a user that might get it.

[Achilleas Koutsou]

We should actually be catching this error before it reaches the depsolver, but it'd be good to have it here too.

[Simon de Vlieger]

Perhaps an unpopular opinion but removing the assertion here will likely lead to a more descriptive exception when the dict is getting used (probably a KeyError) :)

[Achilleas Koutsou]

Resolve by #1412