Lock yarn version to classic because build does not support yarn modern

.yarnrc.yml

@@ -0,0 +1,3 @@
+nodeLinker: node-modules
+
+yarnPath: .yarn/releases/yarn-1.22.19.cjs

package.json

@@ -112,5 +112,6 @@
     "express": "^4.17.1",
     "helmet": "^4.4.1",
     "http-proxy-middleware": "^1.0.6"
-  }
+  },
+  "packageManager": "yarn@1.22.19"
 }