Follow-up from "Move subscription seats details to Apollo"

The following discussions from !182384 (merged) should be addressed:

• @kpalchyk started a discussion:

  suggestion (non-blocking): I missed this previously: we're adding the GraphQL queries on the usage_quotas/seats/ level, while resolvers for them we add on the root usage_quotas/ level. We probably should move these resolvers down to the seats subfolder (currently these queries only work in Seats tab, right?).

  I think the easiest path for now would be to import resolvers from usage_quotas/seats/resolvers into this usage_quotas/shared/resolvers file.

  no need to stop for this, we can do it in a follow-up

• @kpalchyk started a discussion:

  question (non-blocking): can we drop the fetchBillableMemberDetails then?

  can be a follow-up

• @kpalchyk started a discussion:

  suggestion: it feels like we're degrading on the specs as compared to the actions spec we added back here: !150852 (comment 1899698191)

  I think at least covering the hasIndirectMembership: true case is needed. Or we can reproduce all the cases from the action_spec.

  I'm ok to proceed as-is if we have a quick-follow-up on this.

• Could we've added an extra request at some point?

  http://localhost:3000/api/v4/groups/24/billable_members?per_page=20&sort=last_activity_on_desc
  http://localhost:3000/api/v4/groups/24/billable_members?per_page=20&sort=last_activity_on_desc&page=1

• Revert the functionality of not showing any billable members if there's an error