fix: add matchbox package to the docker image

without matchbox package the UI tests do not run as expected

.gitpod.Dockerfile

@@ -5,6 +5,8 @@ USER root
 RUN add-apt-repository universe
 RUN apt update
 RUN apt -y install graphviz
+RUN sudo apt-get update && sudo apt-get install -y matchbox && sudo apt-get clean && sudo rm -rf /var/cache/apt/* && sudo rm -rf /var/lib/apt/lists/* && sudo rm -rf /tmp/*
+
 
 USER gitpod