Start and end activities: Setup experience and macOS MDM migration

[noahtalerman]

• @noahtalerman: Draft PR from hackathon in Boulder CO is here: 29729 host lifecycle events #39764

Goal

User story
As an IT admin,
I want to catch activities webhooks for new macOS, Windows, and Linux setup and macOS MDM migration
so that I can send messages in a Slack channel that helps me monitors how new Mac setup and MDM migration is going.

Changes

Product

• UI changes: Figma wireframes
• CLI (fleetctl) usage changes: No changes
• YAML changes: No changes
• REST API changes: No changes
• Fleet's agent (fleetd) changes: No changes
• Fleet server configuration changes: No changes
• Exposed, public API endpoint changes: No changes
• fleetdm.com changes: No changes
• GitOps mode UI changes: No changes
• GitOps generation changes: No changes
• Activity changes: PR
• Permissions changes: No changes
• Changes to paid features or tiers: macOS setup experience and Fleet's end user migration workflow are Fleet Premium only.
• My device and fleetdm.com/better changes: No changes
• First draft of test plan added
• Other reference documentation changes: No changes
• Once shipped, requester has been notified
• Once shipped, dogfooding issue has been filed

Engineering

• Test plan is finalized
• Contributor API changes: TODO
• Feature guide changes: TODO
• Database schema migrations: TODO
• Load testing: TODO

ℹ️  Please read this issue carefully and understand it. Pay special attention to UI wireframes, especially "dev notes".

QA

Risk assessment

• Requires load testing: TODO
• Risk level: Low / High TODO
• Risk description: TODO

Test plan

Make sure to go through the list and consider all events that might be related to this story, so we catch edge cases earlier.

1. Step 1
2. Step 2
3. Step 3

Testing notes

Confirmation

1. Engineer: Added comment to user story confirming successful completion of test plan.
2. QA: Added comment to user story confirming successful completion of test plan.