I've just come across the same problem.
I simply followed the suggestion from the error message - "Please add log4j-core to the classpath":
- downloaded log4j-core.jar from Maven Central,
- put it into the "ext" directory, next to the log4j-api.jar that was already there.
I've got the same version 2.17.2 (for Workbench/J #129), that can be found in "META-INF/maven/org.apache.logging.log4j/log4j-api/pom.properties" inside log4j-api.jar.
I hope this helps someone.