Fetch full campaign details across the network

1. Invoking the campaigns endpoint with a network account now returns all campaigns across the network.

   (Previously, this would return 0 results.)

2. To reduce the response size, apply paging and sorting.
3. You can also filter for specific campaigns: GET backstage/api/1.0/{network-account}/campaigns/?campaign_ids=123&campaign_ids=456

To fetch basic details for all campaigns across the network, use the campaigns/base endpoint.