Create documentation page about events

[callumforrester]

• Add page about events to developer documentation
• Explain why we need to add new events on top of the event model
• Explain the use of correlation IDs

[callumforrester]

Still to do: make API reference and point to that

[codecov]

Codecov Report

Merging #152 (58ecb40) into main (e8e1fda) will decrease coverage by 8.61%.
The diff coverage is n/a.

❗ Current head 58ecb40 differs from pull request most recent head 6256cea. Consider uploading reports for the commit 6256cea to get more accurate results

@@            Coverage Diff             @@
##             main     #152      +/-   ##
==========================================
- Coverage   83.07%   74.47%   -8.61%     
==========================================
  Files          40       37       -3     
  Lines        1111     1050      -61     
==========================================
- Hits          923      782     -141     
- Misses        188      268      +80     

see 11 files with indirect coverage changes

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[DiamondJoseph]

nit, otherwise LGTM

[DiamondJoseph]

Presumably going to need an update for emitting state events on same topic?

[keithralphs]

Presumably going to need an update for emitting state events on same topic?

Do that as part of addressing #176