Fixing RTC mode enabling check + adding RTC extension lock

cesnet-central/deployments/fullhub.yaml

@@ -152,8 +152,9 @@ singleuser:
 
         # Disables RTC extension. To enable it set this env variable in kubespawner_override
         # to JUPYTERHUB_ALLOW_TOKEN_IN_URL="1"
-        if [ -z JUPYTERHUB_ALLOW_TOKEN_IN_URL ]; then
+        if [ -z "$JUPYTERHUB_ALLOW_TOKEN_IN_URL" ]; then
           jupyter-labextension  disable @jupyter/collaboration-extension
+          jupyter-labextension lock @jupyter/collaboration-extension
         fi
 
         cd .