Name of maven cache image is not right on workshop definiton

Since we created this repository on educates org, we should have updated the location of the maven cache image as it has now a different name `ghcr.io/educates/labs-spring-workshops-maven:latest` from previous incarnation of labs https://github.com/educates/labs-spring-workshops/blob/main/workshops/lab-spring-boot-on-k8s/resources/workshop.yaml#L21