Allow setting leader-election.image via flags/env-variables

This will make it possible to get this value from a separate configmap instead of the normal naiserator.yml config file.

pkg/naiserator/config/config.go

@@ -264,6 +264,7 @@ func init() {
 		"how often to run a full synchronization of all applications",
 	)
 
+	flag.String(LeaderElectionImage, "", "image to use for leader election in deployed applications")
 	flag.Int(MaxConcurrentReconciles, 1, "maximum number of concurrent Reconciles which can be run by the controller.")
 	flag.Int(RateLimitQPS, 20, "how quickly the rate limit burst bucket is filled per second")
 	flag.Int(RateLimitBurst, 200, "how many requests to Kubernetes to allow per second")