Slack block action interactions

Handles Slack block_actions interactions (approve/deny action prompts). Acks immediately and processes the action asynchronously. Request signature is verified via x-slack-signature header.

curl -X POST "http://localhost:3001/api/v1/slack/interactions"

{
  "ok": true
}

{
  "error": "string",
  "message": "string",
  "requestId": "string"
}

{
  "error": "string",
  "message": "string",
  "requestId": "string"
}