Add Fanout payload to SNS messages

[waisingyiu]

What's changed?

Implementation notes

Checklist

General

• [ ] 🤖 Relevant tests added
• [ ] ✅ CI checks / tests run locally
• [ ] 🔍 Checked on CODE

Client

• [ ] 🚫 No obvious console errors on the client (i.e. React dev mode errors)
• [ ] 🎛️ No regressions with existing user interactions (i.e. all existing buttons, inputs etc. work)
• [ ] 📷 Screenshots / GIFs of relevant UI changes included