UI to support showing event data in context of a schema

[joonas-fi]

Benefits:

• Show really helpful debug information in the UI for events (like additional description for the field, possible values for enums etc.)
• Print the domain model associated with the event

Work needed:

• We already have event definitions as machine-readable JSON. Event Horizon would need to be able to access that somehow
• How to discover schema from event path? Schema to list stream patterns like /+/certbus?