After a few days of trial and error, I managed to connect my WSO2 API Manager with my WSO2 Analytics Worker node (both are on the same host). I first spin up the Analytics worker node and then the WSO2 API Manager. After the API Manager is up and running, I can see the following message "INFO {org.wso2.carbon.databridge.core.DataBridge} - user admin connected" in the worker node log. After that I successfully started the Analytics Dashboard node on the same host.
I made some progress. The issue was with the DCR url https://xxxxxxxx.xx:9443/client-registration/v0.15/register I had to change the version to v0.16.
Issue closed