StreamSourceNode is a StreamsGraphNode that is created when InternalStreamsBuilder is requested to add a KStream to a topology.
In other words, StreamSourceNode represents StreamsBuilder.stream and KStreamImpl.through operators.
StreamSourceNode takes the following when created:
Name of the node
Topic names (Collection<String>) or topic pattern (Java’s java.util.regex.Pattern)
void writeToTopology(final InternalTopologyBuilder topologyBuilder)
writeToTopology simply requests the given InternalTopologyBuilder to addSource (per ConsumedInternal and topicPattern or topicNames).