Move `Seat Usage` page from Billing directory to Usage Quotas

Summary

As part of the long-term vision for Seat Usage documented in &5872 (closed) we will move the Seat Usage page from the current location within the group settings > Billing directory, to group settings > Usage Quotas.

Success Criteria

1. Create Seats tab in Usage Quotas
   1. Order of tabs: Seats | Pipelines | Storage
2. Move Seat Usage page from Group>Billing>Seat Usage to Group>Usage
   1. If the design shows any new components to the Seat Usage page, please disregard. The goal of this issue is to move the existing page, not to iterate on the actual page.
3. Leave the See Usage button on the Group>Billing page, when selected, the loaded page should be in the new location under Usage Quotas

Design