Add glossary and style guide

[EmsArnold]

Adds a glossary of terms, and style guide.

Closes #876 and #1481.

Instructions to reviewer on how to test:

1. Do explanations make sense
2. Are all acronyms/abbreviation/terms included which are currently in use
3. Is guidance in style guide well reasoned

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.05%. Comparing base (405e437) to head (53687f7).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1844   +/-   ##
=======================================
  Coverage   99.05%   99.05%           
=======================================
  Files         289      289           
  Lines       11030    11060   +30     
=======================================
+ Hits        10926    10956   +30     
  Misses        104      104           

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.09%. Comparing base (6d91c38) to head (77cf9bc).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1844   +/-   ##
=======================================
  Coverage   99.09%   99.09%           
=======================================
  Files         303      303           
  Lines       11446    11446           
=======================================
  Hits        11342    11342           
  Misses        104      104           

☔ 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.

[oliwenmandiamond]

I think this looks really good and have no objections. Probably need a wider consensus than just myself though

[Villtord]

Thanks it looks great!
I am not a native English speaker so please double check my suggestions :)

[DominicOram]

This is great, thank you! I have added some suggestions but all optional