feat: parallelize LoadTest, MonitorTestnet and ObservabilityStack activities #7
Description
The main idea here is to use signals from LoadTest to tell MonitorTestnet when to stop, so we don't have to depend on arbitrary timeouts to stop the monitoring of a chain.
The only caveat for implementing this technique is that it'd require to split up ObservabilityStack into two activities - one for Prometheus, one for Grafana. This is required since Prometheus is a prerequisite for launching the loadtest (otherwise we're going to have missing metrics for some amount of time).