Stream importer should support Avro file input

The stream importer can import files and generate random documents, but it will be more interesting to import Avro files representing documents.

If we can express a target document schemas in Avro NXP-24325, this can be used as a required input format to mass import documents.

This is a better choice than json, xml or csv because:

• an Avro object container file contains the schema used to write the data
• the file cannot contains invalid data (not respecting the schema)
• the format is as compact as possible