torchx/notebook: added workspacefile magic for use with notebooks

[d4l3k]

This adds the notebook workspace magic/helpers as described in #344

Test plan:

pytest torchx/test/notebook_test.py
pyre

[facebook-github-bot]

@d4l3k has imported this pull request. If you are a Facebook employee, you can view this diff on Phabricator.

[codecov]

Codecov Report

Merging #356 (95b1970) into main (0f81544) will increase coverage by 0.02%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #356      +/-   ##
==========================================
+ Coverage   94.55%   94.58%   +0.02%     
==========================================
  Files          59       60       +1     
  Lines        3084     3101      +17     
==========================================
+ Hits         2916     2933      +17     
  Misses        168      168              

Impacted Files	Coverage Δ
torchx/notebook.py	100.00% <100.00%> (ø)

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[facebook-github-bot]

@d4l3k merged this pull request in a9c1a3d.