[CdapIO] SparkReceiverIO PoC: Read from Spark Receivers via Unbounded

Context:

As a result of the third sprint, we should represent the working SparkReceiverIO PoC with reading via Unbounded functionality

Task Description:

Design and implement the first draft of the SparkReceiverIO package architecture and its child components. Implement a working read example.

Acceptance criteria:

Design of the architecture of the SparkReceiverIO package:

1. Diagram of the package directory structure

1. Sequence diagram for SparkReceiverIO structural components

Working read example with any Custom SparkReceiver.