Remove certificate as required from proxy host

Author: Sander0542

backend/schema/components/proxy-host-object.json

@@ -22,8 +22,7 @@
 		"enabled",
 		"locations",
 		"hsts_enabled",
-		"hsts_subdomains",
-		"certificate"
+		"hsts_subdomains"
 	],
 	"additionalProperties": false,
 	"properties": {