Add Deep Groups Data on Front-end

[asherdrake]

Is your feature request related to a problem? Please describe.

The current solution for Issue #1496 (Group Visualization) involves highlighting Deep Groups of a selected group. However, the frontend Redux state (GroupData) lacks Deep Groups data.

Describe the solution you'd like

Add the Deep Groups data to the root GET /api/groups endpoint in the backend, and add a deepGroups property to the GroupData interface in the frontend.

Describe alternatives you've considered

Add a way to call the already-existing GET /api/groups/deep/groups/:group_id endpoint in the backend from the front-end, but this is inconsistent with current implementation, since Deep Meters are returned as part of the root GET /api/groups endpoint.

Additional context

None