cubicweb-forge #2447099 Convert ticket's "type" into user-definable "labels" [open]

Take example on github. There are issues, issues can have "label" (including "Bug", "Feauture", but also "Documentation", and any user-defined labels for a project). Mainly a kind of tag system.

prioritynormal
typeenhancement
done in<not specified>
closed by<not specified>