_This PR is the direct-to-`main` replacement for #19096, which merged to
a now-defunct feature branch_
## Addresses #19052
- update config, webhook interfaces, mock
- clean up deprecated Sandbox code
- implement Activity Feed Automations Modal and associated logic
- Also addresses #19284

- [x] Changes file added for user-visible changes in `changes/`
- [x] Manual QA for all new/changed functionality
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Co-authored-by: Jacob Shandling <jacob@fleetdm.com>