Returns a single campaign by campaign_uuid, scoped to the authenticated account. Alongside the campaign metadata the response carries eds_uuid and footer_uuid -- the email delivery system (sending domain) and footer currently set as the campaign's defaults; these propagate to emails created inside the campaign's sequences. num_sequences is the count of non-deleted sequences. The returned eds_uuid/footer_uuid are the values to echo back (or change) on an update_campaign call. This route accepts either GET (with campaign_uuid as a query-string parameter) or POST (with the JSON body shown here).