Upgrade to Yarn Berry

.gitignore

@@ -10,3 +10,10 @@ public/config.json
 backend/synapse_tmp/*
 /coverage
 yarn-error.log
+/.pnp.*
+/.yarn/*
+!/.yarn/patches
+!/.yarn/plugins
+!/.yarn/releases
+!/.yarn/sdks
+!/.yarn/versions

.yarnrc.yml

@@ -0,0 +1 @@
+nodeLinker: node-modules

package.json

@@ -127,5 +127,6 @@
   "resolutions": {
     "@livekit/components-core/rxjs": "^7.8.1",
     "matrix-widget-api": "1.11.0"
-  }
+  },
+  "packageManager": "yarn@4.7.0"
 }