Phone-home configuration

[sweetlandj]

Implement a REST API that will enable remote Platibus instances to request configuration from a primary instance or configuration server. In addition, provide an IPlatibusConfiguration implementation that will make this call and retrieve configuration from the remote server, as well as a ConfigurationSection that can be used to declaratively specify the base URIs of the primary instance / configuration server. Finally, provide an ISubscriptionTrackingService that will POST or DELETE subscription info to the primary instance / configuration server as it is updated.

[tdbrian]

Started working on project around this https://github.com/tdbrian/Platibus.Registry. It has both a REST API and web UI for for managing shared configuration in a single registry as well as some diagnostic UI tools. Looking into adding some additional tools for creating shared contracts and code gen similar to Confluent schema registry for Kafka https://docs.confluent.io/current/schema-registry/index.html#avro-background.