Top-level supervisor managing Fleet queues, Broadway pipelines, and the BEAM ticker.

Example Configuration

children = [
  MyApp.Repo,
  {Fleet,
   repo: MyApp.Repo,
   run_ticker: true,
   queues: [
     default: [concurrency: 10],
     mailers: [concurrency: 20, poll_interval: 50]
   ]}
]