Add new field type for logical values

[jacobcook1995]

This PR adds a new field type for logical values (i.e. cases where data can be either true or false).

Code changes are minimal (because I could follow the existing pattern), but do need to be sanity checked

I've also added description of this new field type to the docs, which I could do with some feedback on.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.28%. Comparing base (dce2ecf) to head (ab4bac0).
⚠️ Report is 10 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #230      +/-   ##
===========================================
+ Coverage    81.12%   81.28%   +0.15%     
===========================================
  Files           14       14              
  Lines         3544     3558      +14     
===========================================
+ Hits          2875     2892      +17     
+ Misses         669      666       -3     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[davidorme]

That all looks very clear.