Add a JupyterLab extension for the memory usage status bar item

[jtpio]

See jupyterlab/jupyterlab#9363

In JupyterLab 3.0, users will still get the memory usage status bar item on pip install nbresuse.

Leveraging the federated (also called "pre-built" / "dynamic") extensions in JupyterLab 3.0: https://jupyterlab.readthedocs.io/en/latest/developer/extension_dev.html#goals-of-the-federated-extension-system

Displays the indicator twice for now, until JupyterLab removes it from the core extensions Edit: This is not the case anymore when updating to 0.4.0 without enabling the /metrics endpoint.

TODO

• Bootstrap the extension
• Port the code from lab
• Enable strict null checks in tsconfig
• Add dev instructions to the readme
• Adopt the monorepo structure from the start
• Rename the extension to @jupyter-server/resource-usage
• Credit the original authors. The status bar was added to core in this squashed commit: jupyterlab/jupyterlab@d158501#diff-be21886035b24ea232455cba02fb349aa53c352e0bfaa55c5a53410fc616be5b. Here we could have a single commit with multiple Co-authored-by: name <[email protected]> entries

[jtpio]

Rebased to include the renaming from nbresuse to jupyter-resource-usage from #74

[ajbozarth]

I wanted to give this a deeper review, but I have other commitments prior to EOY so for now I can say I tested this locally and it it worked as expected and on an initial pass the code look good. So I'll give this a soft approval

[jtpio]

Thanks @ajbozarth.

Just pushed a couple more changes to:

• Add the Jupyter Server extension config file: jupyter server extension list
• Move the config to the jupyter-config folder