Make it so that subquestions count toward filters and sorts

[ryooan]

Currently if you use a filter in the feed, it only applies to top level questions / posts.

But this misses subquestions that apply to the filter. For example, when admins use the "Pending Resolution" filter we can't see subquestions that need resolved in the feed. We have to track / find these through a spreadsheet off the platform, which isn't ideal.

I think it would be much nicer if when you used any filter or sort the details of subquestions determine whether a group question appears.

This could potentially have downsides we might need to check for or consider (for example if a new subquestion opens on an existing group, it would then show up in the "new" feed, though this is probably desirable honestly).