BD-3712 Update message engagement event abort type

[rachel-feinberg]

Why are you making this change? (required)

Update the message engagement events definition for "abort_type" to remove example values. There are currently about 30 example values, and the current definition implies there are only a few.

Related PRs, issues, or features (optional)

BD-3712

Feature release date (optional)

• N/A

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[internetisaiah]

LGTM, but not sure if you need to verify with a SME on the details. Feel free to merge whenever you're ready 👍🏽