Hi Brandon,
The foreach processor is for preprocessing documents before they're indexed in Elasticsearch, and no such functionality exists in Kibana. I'm a bit confused about what you're asking for here.
Now, for each meetingId I'd like to create a visualization that presents data of the users
It sounds like you want to dynamically generate visualizations based on the data set returned by a query. Kibana doesn't support this in the UI, but you could write some scripts or use automation tools to do this. Here's some information about the API you'll need to hit: https://github.com/elastic/kibana/pull/11632.
You can GET a visualization using this API to see what kind of payload you'd need to send to create it. For example:
curl -H "Content-Type: application/json" -H "kbn-xsrf: true" http://localhost:5601/api/saved_objects/visualization/{visualization ID}
You can find the visualization ID by opening up the visualization in Kibana and looking for the ID in the URL:
http://localhost:5601/app/kibana#/visualize/edit/{visualization ID}
Hope this helps,
CJ