feat(hook): Deliver events to integrations

[prathshenoy]

Summary

What:

• Consume lifecycle events from a durable queue and hand each one to every integration wired for the deployment, retrying and then dead-lettering the ones that keep failing.
• Record every dead-lettered event with its full payload and failure reason, and count it on a metric meant to page.

Why:

• Keep a slow or broken integration from stalling or failing the work that triggered it.
• Make a lost notification recoverable and impossible to miss, since nothing else in the system notices when one goes missing.

Test Plan

• Add unit tests.

Revert Plan

• Revert this PR. No service constructs the dispatcher or subscribes to the hook topic.

Issues

• CODEM-416

Stack

1. feat(hook): Add contract for lifecycle events #606
2. @ feat(hook): Deliver events to integrations #607
3. feat(orch): Consume hook events #608