Defines a Stargate.Receiver.Processor module as a GenStage process under the consumer or reader supervision tree.

The processor stage performs the message handling step for all messages received on the connection by storing and calling the application's handler module on each message received.

To better handle complex or long-running operations when handling messages, the processor stage can be scaled horizontally and takes care of the necessary subscriptions both upstream and downstream within the GenStage pipeline.

During initialization, the processor stage stores several pieces of information in its process dictionary that are available to the application's message handler module when handling messages if necessary including the topicc, namespace, tenant, and persistence of the connection.