Use the IssueFinder to filter by labels in the API
Issues are filtered by labels by a custom filter method
filter_issues_labels which matches if any of the labels matches. However, the
IssueFinder already provides a functionality to filter by labels but only matches if all labels matches.
IssueFinder label filtering method in the issues to avoid duplication. The
/groups/:id/issues already uses the
IssueFinder therefore. Changing this behavior would also unify the API behavior.