Adding ImagePullPolicy config option to OSM Charms

Change-Id: I04ad8444088e8a360755dc4e22b7ea53942682b2
Signed-off-by: sousaedu <eduardo.sousa@canonical.com>
diff --git a/installers/charm/ro/config.yaml b/installers/charm/ro/config.yaml
index 0d3c9a0..5bb0362 100644
--- a/installers/charm/ro/config.yaml
+++ b/installers/charm/ro/config.yaml
@@ -70,3 +70,9 @@
         name: name of the file for the certificate
         content: base64 content of the certificate
       The path for the files is /certs.
+  image_pull_policy:
+    type: string
+    description: |
+      ImagePullPolicy configuration for the pod.
+      Possible values: always, ifnotpresent, never
+    default: always