docs: Add simple devices and plans for use in tutorials

[abbiemery]

With the removal of dodal as a dependency, we need to provide some simple devices and plans in order to follow through the tutorials. These are getting cleaned up in #1564.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.93%. Comparing base (b767635) to head (c86ab86).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1577   +/-   ##
=======================================
  Coverage   95.93%   95.93%           
=======================================
  Files          44       44           
  Lines        3300     3300           
=======================================
  Hits         3166     3166           
  Misses        134      134           

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[abbiemery]

Is there a better place for this to live?

[tpoliaw]

utils would make the most sense if there's a way of getting it working without import order issues

[abbiemery]

utils but not include it in the __all__ ?

[abbiemery]

After a lot of rabbit holes, I went back to using optional dependencies for the demo. I don't think the config should live in that module though, I will put it just in the docs.

[abbiemery]

If you can think of an actually useful test for the devices, let me know