🔧(devx) configure a TURN server on the local LiveKit dev stack

Wire a TURN server into the local LiveKit server used by the dev
stack, so ICE negotiation has more candidate types available during
local testing.

Makes it easier to reproduce connectivity scenarios that would
otherwise only show up on stricter networks in production.

docker/livekit/config/livekit-server.yaml

@@ -8,3 +8,16 @@ webhook:
   api_key: devkey
   urls:
       - http://app-dev:8000/api/v1.0/rooms/webhooks-livekit/
+
+turn:
+  enabled: true
+  domain: turn.127.0.0.1.nip.io
+  udp_port: 3478
+  tls_port: 0
+  external_tls: false
+  relay_range_start: 30000
+  relay_range_end: 30100
+  allow_restricted_peer_cidrs:
+    - 192.168.0.0/16
+    - 172.16.0.0/12
+