A Task to attach a logger exporter for health-checker telemetry

Attaches a telemetry handler which writes out how far a producer is behind the head of the stream to the logger.

This task can be started in a supervision tree such as an app's application supervision tree:

def start(_type, _args) do
  children = [
    Beeline.HealthChecker.Logger,
    MyApp.MyBeelineTopology
  ]
  opts = [strategy: :one_for_one, name: MyApp.Supervisor]
  Supervisor.start_link(children, opts)
end

The log messages are 'info' level in a format of the producer name concatenated with "is caught up." if the producer's current stream position matches the latest available stream position and a 'warn' level message with "is behind: n events." when the producer is behind, with n being the number of events. The log messages also include metadata fields :event_listener - the name of the producer - and delta: the number of events by which the producer is behind.