How configure Channel (MQTT) topic filter using CloudFormation?

I want to replicate using CloudFormation the IOTA environment configured by following the steps in the 'AWS IoT Analytics Console Quickstart Guide'. Problem is I can't find out how to configure the IoT Core (MQTT) topic filter for the channel (step 6). How can I do this?

The docs for AWS::IoTAnalytics::Channel did not help, neither do the tempates in https://aws.amazon.com/blogs/iot/introducing-aws-cloudformation-support-for-aws-iot-analytics/

I think I might be missing something fundamental here (e.g. should I be looking for a MQTT 'Message Broker' component to which I should connect my channel??)

Related question, is there a way to dynamically (i.e. programmatically) update this type of infrastructure setup for a live configuration?

Thanks in advance!

Edited by: fpet on May 2, 2020 12:08 PM

Edited by: fpet on May 2, 2020 2:24 PM