Add Jupyter plugin support to caliban [draft]

[sritchie]

This PR is here to begin figuring out how to do this for jupyter and jupyterlab.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 50.44%. Comparing base (0bd5667) to head (adbd647).
Report is 48 commits behind head on main.

Files with missing lines	Patch %	Lines
caliban/platform/notebook.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #19      +/-   ##
==========================================
- Coverage   50.60%   50.44%   -0.16%     
==========================================
  Files          28       28              
  Lines        2897     2898       +1     
==========================================
- Hits         1466     1462       -4     
- Misses       1431     1436       +5     

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[sritchie]

I've looked more into this, and it won't work to do what I've done in the PR! That's because you need to run jupter lab build after you change the directory.

I think we'll need to explicitly support this by adding a jupyter_plugins list to .calibanconfig, and then do this to get them installed without blowing up the base image:

jupyterlab/jupyterlab#4930

If we want to be REALLY pro, we can do a multistage build for this step. That is probably the right approach.