Simplify the jupyter kernelspec setup

[davidorme]

Description

This removes the ve_python3 specific kernel for jupyter and falls back to poetry run/shell setting the jupyter kernelspec to point to the active poetry venv for the project.

The tests below and RTD all work, showing this simplification works as expected:
https://virtual-ecosystem.readthedocs.io/en/427-simplify-the-jupyter-kernelspec-setup/

Closes #427

Type of change

• New feature (non-breaking change which adds functionality)
• Optimization (back-end change that speeds up the code)
• Bug fix (non-breaking change which fixes an issue)

Key checklist

• Make sure you've run the pre-commit checks: $ pre-commit run -a
• All tests pass: $ poetry run pytest

Further checks

• Code is commented, particularly in hard-to-understand areas
• Tests added that prove fix is effective or that feature works

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.60%. Comparing base (0ccb1c7) to head (73686c6).

Additional details and impacted files

@@           Coverage Diff            @@
##           develop     #429   +/-   ##
========================================
  Coverage    94.60%   94.60%           
========================================
  Files           70       70           
  Lines         3744     3744           
========================================
  Hits          3542     3542           
  Misses         202      202           

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[jacobcook1995]

LGTM, just a couple of minor queries.