Document upcoming changes to events payload

[roman-y-wu]

Closes#3665

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.23%. Comparing base (84a0945) to head (2640f20).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@ Coverage Diff @@## master #3667 +/- ##
=======================================
Coverage 91.23% 91.23% =======================================
Files 185 185 Lines 16421 16421 =======================================
Hits 14982 14982 Misses 1254 1254 Partials 185 185 

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[gmlewis]

Thank you, @romanywu!
LGTM.

Awaiting second LGTM+Approval from any other contributor before merging.

@alexandear or @stevehipwell - might one of you be available for a code review? Thank you!

[alexandear]

Please remove (Issue #3665) from PR's title and add Closes #3665 to description.

[stevehipwell]

Thanks @romanywu this looks really good, just waiting on the PR changes @alexandear asked for before I approve.

@gmlewis if you want to get this merged you should be able to update the title and PR body.

[roman-y-wu]

Please remove (Issue #3665) from PR's title and add Closes #3665 to description.

✅

[stevehipwell]

LGTM

[gmlewis]

Thank you, @romanywu, @alexandear, and @stevehipwell!
Merging.