Add Play HTTP Secret Key as env variable in deployment

gcloud/feed-service/feed-service-deployment.yaml

@@ -26,6 +26,8 @@ spec:
               value: "true"
             - name: JWT_PRIVATE_KEY
               value: "yB/uX5KdyjHN9P34IE49HxAcrlQ4gfvpVJEzGbo5E/I="
+            - name: PLAY_HTTP_SECRET_KEY
+              value: "DUvbrcM2AbuB7oXboI1x`ZI_?1Iou>/ch2@lFXfrvVkWlHuA848y?GyR/0i2Ma:A"
 ---
 apiVersion: v1
 kind: Service