Enable Real Time Collaboration on DataHub

- Bump up JupyterLab to get latest bugfixes
- Enable the --collaborative flag
- Install jupyterlab-link-share, required to generate the link
  you can give others to collaborate with you. It adds a
  'Share' menu item to JupyterLab, and also a 'Copy downloadable link'
  item to the context menu. More info at https://pypi.org/project/jupyterlab-link-share/

infra-requirements.txt

@@ -11,7 +11,8 @@
 notebook==6.4.5
 # FIXME: Conflicts with jupyter-server-proxy somehow
 jupyter-client<7.0
-jupyterlab==3.2.2
+jupyterlab==3.2.4
+jupyterlab-link-share==0.2.1
 nbconvert==6.1.0
 retrolab==0.3.13
 nbgitpuller==1.0.2