1. determine if schema registry supports aggregated avro schema

Schema registry supports schema references starting with version 5.5.0

A work-around that consists of generating composite avro schemas
before upload to registry is implemented in schema-registry mvn plugin v5.3.x

 confluentinc/schema-registry#855


https://stackoverflow.com/questions/40854529/nesting-avro-schemas
- post suggesting that schema-registry supports references between schemas if those are registered with a single
union type



2. assuming schema aggregation not supported - solution based on build-time aggregation

Solution: Use velocity to include the schema of a field at the location of
the field definition in the dependent schema.
Processing is performed at build time ( generate-sources phase), before avro schema generation.

PoC : example-avro-agg-build


https://groups.google.com/forum/#!topic/confluent-platform/pey5-AS1NSE
- post suggesting to aggregate schemas externally