Load DNS overwrite config on startup

I recently noticed that DNS overwrite does not happen. There are messages in logs: "No DNS overwrite for <REDACTED>", but I definitely have configured DNS overwrithng. I think it's because DNS overwriting config is not loaded when ma1sd starts up.
Documented here: https://github.com/ma1uta/ma1sd/blob/master/docs/features/authentication.md#dns-overwrite and here: https://github.com/ma1uta/ma1sd/blob/master/docs/features/directory.md#dns-overwrite

src/main/java/io/kamax/mxisd/config/MxisdConfig.java

@@ -359,6 +359,7 @@ public MxisdConfig build() {
         getAuth().build();
         getAccountConfig().build();
         getDirectory().build();
+        getDns().build();
         getExec().build();
         getFirebase().build();
         getForward().build();