Adding ImagePullPolicy config option to OSM Charms

Change-Id: I04ad8444088e8a360755dc4e22b7ea53942682b2
Signed-off-by: sousaedu <eduardo.sousa@canonical.com>
diff --git a/installers/charm/pla/config.yaml b/installers/charm/pla/config.yaml
index 1820188..75b19d8 100644
--- a/installers/charm/pla/config.yaml
+++ b/installers/charm/pla/config.yaml
@@ -27,3 +27,9 @@
   mongodb_uri:
     type: string
     description: MongoDB URI (external database)
+  image_pull_policy:
+    type: string
+    description: |
+      ImagePullPolicy configuration for the pod.
+      Possible values: always, ifnotpresent, never
+    default: always