Add build flag for webpush

server/server_webpush.go

@@ -15,6 +15,10 @@ import (
 )
 
 const (
+	// WebPushAvailable is a constant used to indicate that WebPush support is available.
+	// It can be disabled with the 'nowebpush' build tag.
+	WebPushAvailable = true
+
 	webPushTopicSubscribeLimit = 50
 )