Adding ImagePullPolicy config option to OSM Charms

Change-Id: I04ad8444088e8a360755dc4e22b7ea53942682b2
Signed-off-by: sousaedu <eduardo.sousa@canonical.com>
diff --git a/installers/charm/keystone/config.yaml b/installers/charm/keystone/config.yaml
index 9a7acd5..945ea48 100644
--- a/installers/charm/keystone/config.yaml
+++ b/installers/charm/keystone/config.yaml
@@ -42,6 +42,12 @@
     type: string
     description: Ingress URL
     default: ""
+  image_pull_policy:
+    type: string
+    description: |
+      ImagePullPolicy configuration for the pod.
+      Possible values: always, ifnotpresent, never
+    default: always
   region_id:
     type: string
     description: Region ID to be created when starting the service