Set packageManager (#55)

Prevent dependabot of using a wrong yarn version that may result in yarn.lock format changes

Author: fcollonval

package.json

@@ -52,6 +52,7 @@
         "watch:labextension": "jupyter labextension watch .",
         "watch:src": "tsc -w --sourceMap"
     },
+    "packageManager": "yarn@3.5.0",
     "dependencies": {
         "@jupyterlab/application": "^4.0.0",
         "@jupyterlab/apputils": "^4.0.0",