cluster/admitomatic: allow whitelist-source-range

Without this, cert-manager get stuck.

Deployed to prod.

Change-Id: I356cd44f455b6f4aecea9ae396f6a05e1a727859
diff --git a/cluster/admitomatic/ingress.go b/cluster/admitomatic/ingress.go
index a1d57a5..6b8a365 100644
--- a/cluster/admitomatic/ingress.go
+++ b/cluster/admitomatic/ingress.go
@@ -210,6 +210,8 @@
 		"proxy-body-size":  true,
 		"ssl-redirect":     true,
 		"backend-protocol": true,
+		// Used by cert-manager
+		"whitelist-source-range": true,
 	}
 	prefix := "nginx.ingress.kubernetes.io/"
 	for k, _ := range ingress.Annotations {