Execute custom query and notify via Slack

Create a YAML or JSON with all custom queries to execute every x time:

Example:

```
queries:
- description: "purchase by hours"
  query: "SELECT count(id) FROM purchases WHERE created_at >=..."
  schedule: every 1 hour
  warning: 10
  alert: 0
  channel: kpi
```

Related projects:
- https://github.com/rakanalh/scheduler
- https://github.com/nlopes/slack
