Add streaming find endpoint

[joelochlann]

todo

• [ ] make it close the connection once all hits have been sent
• [ ] wire up client

other examples

• https://github.com/guardian/typerighter/pull/20
• https://github.com/guardian/grid/blob/main/thrall/app/lib/MigrationSourceWithSender.scala
• https://1545.deno.dev/