Enforce filter-specific sorting rules for filter options

[elizamander]

When a user views the list of options for filtering by size, the sort appears to be random:

For some options like shoe size, we can get away with filtering the options numerically. However, t-shirt size has a bespoke sort that all users expect: XS > SM > MD > LG > XL . The CMS should have this capability, and all filters for our final product set should be sorted in a way that users expect. This could possibly be an admin capability if it isn't already?

[Burnett2k]

This will probably warrant further discussion, since we're no longer using shirts. I can try and derive the actual ask here from comments, but I think it would be more productive to discuss in a meeting.