refactor: parse matchspec url into NamedChannelOrUrl [skip ci]

[wolfv]

I think it would be good to stop the weird channel parsing in matchspecs because it's subtly wrong. We always create a "default" channel config.

However, now we have two problems:

• we need a channel config in the resolvo context so that we can continue comparing matchspecs
• the matches(...) function needs a second matches_with_channel_config(...) function or a second parameter with a optional channel config to properly evaluate the channels from config.

Wanted to ask for early feedback before going down this path further.

[baszalmstra]

Perhaps we should have a "ResolvedMatchSpec" and a non-resolved one. Also a big refactor..