Allow passing a custom command

This to e.g. be able to open a bash shell for manual builds with 'make -j'

container/start-ubuntu-container.sh

@@ -23,6 +23,8 @@
 SCRIPT_LOCATION=$(realpath "$(dirname "${BASH_SOURCE[0]}")")
 CELIX_REPO_ROOT=$(realpath "${SCRIPT_LOCATION}/..")
 
+CONTAINER_COMMAND=${1:-}
+
 # Start a container with all the Celix dependencies pre-installed
 #   --privileged            to allow the unit tests to change thread priorities
 #   --net=host              is used to allow e.g. communication with etcd
@@ -33,5 +35,5 @@ podman run -it --rm --privileged \
            --volume "${CELIX_REPO_ROOT}":"${CELIX_REPO_ROOT}" \
            --workdir "${CELIX_REPO_ROOT}" \
            --security-opt label=disable \
-           apache/celix-dev:2.4.0-ubuntu
+           apache/celix-dev:2.4.0-ubuntu ${CONTAINER_COMMAND}