molecule scenario to test upgrading from releases

Provide a separate scenario to install the last release, then update to
the current one.
Also includes improved deployment verification (check if uploading a
.txt through the API works).

ansible/molecule/fresh/converge.yml

@@ -0,0 +1,7 @@
+---
+- name: fresh installation
+  hosts: all
+  tasks:
+    - name: install paperless-ng with default parameters
+      include_role:
+        name: ansible