add dedicated config for local development environment

Author: fkwp

config/config.devenv.json

@@ -0,0 +1,15 @@
+{
+  "default_server_config": {
+    "m.homeserver": {
+      "base_url": "http://synapse.localhost:8008",
+      "server_name": "synapse.localhost"
+    }
+  },
+  "livekit": {
+    "livekit_service_url": "http://localhost:8080"
+  },
+  "features": {
+    "feature_use_device_session_member_events": true
+  },
+  "eula": "https://static.element.io/legal/online-EULA.pdf"
+}