docs: optimise building with html-tutorial support

[bjlittle]

🚀 Pull Request

Description

Been meaning to do this for a while now ...

This pull-request optimises documentation building by adding an option to control whether the tutorial jupyter notebook code cells are executed. Not executing notebook cells can make a significant saving at build time, as typically our notebooks will be rich in image rendering, and as we add more content this will become more expensive.

This is a welcome optimisation, particularly when using the make html-noplot workflow e.g., building the docs to eyeball a pull-request changelog contribution should be a slick experience for a fast contributor turnaround.

Note that, we now have the following behaviours:

Command	Doc-string Images	Gallery Images	Tutorial Images
make doctest	❎	❎	❎
make html	☑️	☑️	☑️
make html-docstring	☑️	❎	❎
make html-gallery	❎	☑️	❎
make html-noplot	❎	❎	❎
make html-tutorial (†)	❎	❎	☑️
make linkcheck	❎	❎	❎

† - This is a new Makefile build command.

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.28%. Comparing base (6e26f58) to head (6620ebe).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1146   +/-   ##
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  Coverage   91.28%   91.28%           
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  Files          58       58           
  Lines        2939     2939           
=======================================
  Hits         2683     2683           
  Misses        256      256           

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