Add token management

[brichet]

Fix #825 by adding an optional token parameter when running Voila. Token must be filled manually in command line, it is not automatically generated. The token parameter must be provided in VoilaHandler and VoilaTreeHandler URL, otherwise a 404 error is thrown.

[github-actions[bot]]

:point_left: Try it on binder (branch brichet/voila/token_management_0.3.0a2)

[github-actions[bot]]

:point_left: Try it on binder (branch brichet/voila/token_management_0.3.0a2)

[majidaldo]

wouldn't jupyter be a better place to handle this?

[brichet]

Jupyter already handles this in each application :

• NotebookApp.Token for Jupyter Notebook
• ServerApp.Token for Jupyter Lab

This pull request is basically a copy of what is done in Jupyter to bring the feature to Voilà.

[brichet]

Superseded by https://github.com/voila-dashboards/voila/pull/1308