Add Customization Options to DERP Map entry of integrated DERP server (#1565)

Co-authored-by: Alexander Halbarth <alexander.halbarth@alite.at>
Co-authored-by: Bela Lemle <bela.lemle@alite.at>
Co-authored-by: Kristoffer Dalby <kristoffer@dalby.cc>

config-example.yaml

@@ -94,6 +94,16 @@ derp:
     #
     private_key_path: /var/lib/headscale/derp_server_private.key
 
+    # This flag can be used, so the DERP map entry for the embedded DERP server is not written automatically,
+    # it enables the creation of your very own DERP map entry using a locally available file with the parameter DERP.paths
+    # If you enable the DERP server and set this to false, it is required to add the DERP server to the DERP map using DERP.paths
+    automatically_add_embedded_derp_region: true
+
+    # For better connection stability (especially when using an Exit-Node and DNS is not working),
+    # it is possible to optionall add the public IPv4 and IPv6 address to the Derp-Map using:
+    ipv4: 1.2.3.4
+    ipv6: 2001:db8::1
+
   # List of externally available DERP maps encoded in JSON
   urls:
     - https://controlplane.tailscale.com/derpmap/default