def __init__(config, success_channel, error_channel, metrics, **kwargs):
Initialize a runnable plugin.

        Args:
            config (dict): Plugin-specific configuration.
            success_channel (asyncio.Queue): A sink for successfully processed
                IEventMessages.
            error_channel (asyncio.Queue): A sink for IEventMessages that were
                not processed due to problems.
            metrics (obj): Optional obj used to emit metrics.