Hide DNS in client configuration if not set

wg_dashboard_backend/templates/peer.j2

@@ -1,7 +1,9 @@
 [Interface]
 Address = {{ data.peer.address }}/{{ data.server.subnet }}{%- if is_ipv6 -%},{{ data.peer.v6_address }}/{{ data.server.v6_subnet }}{%- endif %}
 PrivateKey = {{ data.peer.private_key }}
+{% if data.peer.dns %}
 DNS = {{ data.peer.dns }}
+{% endif %}
 
 [Peer]
 PublicKey = {{ data.server.public_key }}