fix queing key for start messages

[fixes #43512503]
Return droplet state over nats.

Listen to and respond to request `healthmanager.droplet` with a json
object containing all healthmanager data about the droplet.

The request message format is:

topic: healthmanager.droplet
payload: { "droplets" => [<droplet_id> , ... ] }

Intended for exploration/debugging.