Metrics. Use Akka / Kafka so we don't block whilst writing to metrics table.

[simonredfern]

Use Akka / Kafka so we don't block whilst writing to metrics table.

Also, we might want to add a connector so that the metrics_connector can be akka_rdbms, akka_elastic_search etc.

[constantine2nd]

Current state use a separate thread whilst writing to metrics table. It's fire and forget scenario. We can use Akka as the middleman in order to unify API for metrics.