Endpoint providing status of "Home assistant is starting..."

If hass was to expose an endpoint providing the status during start-up that would be very helpful for those of us that are running it in HA environments, such as clusters.

This allows for an orchestrator to do a healthcheck waiting for startup to complete prior to redirecting traffic to the new instance and then killing the previous one. At the moment rolling-updates always have some downtime since startup time is not entirely predictable.