Allow a list to be composed of multiple ORed labels
Description
Currently when setting up issue boards it is difficult to create issue boards with different purposes. As an example the default issue board is development and in that case between the backlog and done typically you would have lists for development, and testing and done includes things that have been done.
If you are doing planning you would typically have your backlog of unplanned issues and lists for planning, it might be priorities you want to assign the issues to or teams like backend or ux. When you are doing planning you don't care so much about issues that have the development or testing label because they are "Done" as far as planning is concerned, and you don't want them to show up in your backlog.
Proposal
When creating a new list allow users to select more than one label for the list. These labels are then ORed together for the purpose of displaying what is in that list. So if you had a "Development" label and a "Testing" label on a list if an issue has either label it would display in that list.
When you take this proposal and add #23917 (closed) which would allow you to remove the done and/or the backlog lists you have a very powerful way of configuring what issues show up in which issue boards.
Another way to implement this would be to always keep the backlog and done list, but make them configurable as described above and all other lists would work as normal. In both cases the goal would be accomplished, which is to allow Issue boards to only contain issues that are relevant to that issue board.