Fix #295: Prosody: disabling message carbons for anonymous users.

Anonymous users can't use carbons, as they cannot connect with multiple
tabs on the same anonymous account.
So we disable carbons on the anonymous virtualhost, to improve
performances.

See here for some performances tests: https://github.com/JohnXLivingston/livechat-perf-test/tree/main/tests/50-anonymous-carbons

server/lib/prosody/config/content.ts

@@ -211,6 +211,9 @@ class ProsodyConfigContent {
     this.anon = new ProsodyConfigVirtualHost('anon.' + this.prosodyDomain)
     this.anon.set('authentication', 'anonymous')
     this.anon.set('modules_enabled', ['ping'])
+    this.anon.set('modules_disabled', [
+      'carbons' // carbon make no sense for anonymous users, they can't have multiple windows
+    ])
     if (autoBanIP) {
       this.anon.add('modules_enabled', 'muc_ban_ip')
     }