downloads: split file and containers (#13581)

Splits the definitions into two dicts, while joining then for now to
preserve the downloads dict.

Update all consumers of the variables, which are roughly:
- manual includes of the download role (which will be removed in the
  short future)
- install tasks using the resolved 'dest' to find the artefacts

This will make further division of the downloads role easier.

roles/network_plugin/cni/tasks/main.yml

@@ -9,7 +9,7 @@
 
 - name: CNI | Copy cni plugins
   unarchive:
-    src: "{{ downloads.cni.dest }}"
+    src: "{{ downloads_file.cni.dest }}"
     dest: "/opt/cni/bin"
     mode: "0755"
     owner: "{{ cni_bin_owner }}"