Allow filtering by list of values and wildcard

[danielhuppmann]

The current implementation of CodeList.filter() allows to select by a tag-value combination - however, it is not possible to select by a list, and it is not possible to do wildcard-matching (like pyam).

For example, it would be useful to support the following

RegionCodeList.filter(hierarchy=["R5", "R9"])
VariableCodeList.filter(variable="Final Energy|*")

[danielhuppmann]

I guess that there are synergies in implementation with #416

[phackstock]

it is not possible to select by a list

To be precise, it is possible to select by a list, it is just currently applied literally, so your example for hierarchy would match if for all regions with hierarchy=["R5", "R9"].
So what we'd need to change the logic around and treat a list input as "match true if any of the values" match.

This would leave the question though what we would do if we actually wanted to literally filter for a list match. Maybe an additional keyword ...? Or we just don't offer this functionality.

I'd also suggest doing this in two PRs (one for lists, one for the wildcard) for a cleaner separation.