Updated promtail to include global image pull policy

Package Merge Request

Package Changes

1. Updated promtail values.yaml file to include global imagePullPolicy
2. Updated image_pull_policy doc to include promtail override values

For Issue

Closes #980 (closed)

chart/templates/logging/promtail/values.yaml

@@ -5,6 +5,13 @@
 {{- define "bigbang.defaults.promtail" -}}
 hostname: {{ .Values.hostname }}
 
+initContainer:
+  image:
+    pullPolicy: {{ .Values.imagePullPolicy }}
+
+image:
+  pullPolicy: {{ .Values.imagePullPolicy }}
+
 openshift: {{ .Values.openshift }}
 
 istio: