How to get glue to discover an eventbridge payload for use in CDK gluetable deployment?

The crawler is for data, not likely to work well on metadata like that.
You could for instance run an AWS Lambda that reads the json event using pandas (which will infer the schema).

However, my advice is not to deploy tables (at least tables that evolve) using CDK, let the code/crawlers maintain it. What it sounds you are trying to do (coordinate CDK deployments with tables changes is going to be problematic)