For Kafka - just build something based on metrics from our Extension - https://www.dynatrace.com/support/help/technology-support/dynatrace-extensions/supported-out-of-the-...
For Cassandra- this is what we have for our performance engineering team to observe Cassandra instances we run in Dynatrace:
I have tried to find a template dashboards. I am going to create dashborads from the scratch based on the collected metrics. Thanks for the reference screenshot.