chore: add flow._destroyPublishedAll helper for E2E tests

[jessicamcinchak]

Now that flows are published on create, we need to add additional cleanup steps to our E2E API regression tests. There will also now be instances of more than one published flow associated with a flow during a single test, so it's ideal to have a destroyPublishedAll helper here.

Currently failing with error: Error: Foreign key violation. update or delete on table "users" violates foreign key constraint "published_flows_publisher_id_fkey" on table "published_flows"

{
  "response": {
    "errors": [{
      "message": "Foreign key violation. update or delete on table \"users\" violates foreign key constraint \"published_flows_publisher_id_fkey\" on table \"published_flows\"",
      "extensions": {
        "path":"$",
        "code":"constraint-violation"
      }
    }],
    "status":200,
    "headers":{}
  },
  "request": {
    "query": "mutation DestroyAllUsers {
          deleteUsers: delete_users(where: { id: { _is_null: false } }) {
            affectedRows: affected_rows
        }
      }
    "
  }
}

[RODO94]

First time looking into this _is_null:false condition, cool

[RODO94]

Tested locally and all works for me