update methods "export_collector_value" and "write_to_kafka" parameters and return type of "export_collector_value".

"TelemetryBackend" tests "test_get_kafka_configs()", "test_get_kafka_configs_a()" and "test_export_collector_value()" are added.

NodeExporterProducer: Implementation of Producer: Read from NodeExporter endpoint and writes on Kafka topic