Fix maintenance task

The function was defined but never called, resulting in immediate exit
of the maintenance script.  Fix this, also add a configuration build-arg and
ENV to control the cleaning interval.

Signed-off-by: Chris Evich <chris_gitlab@icuc.me>

Containerfile

@@ -122,7 +122,10 @@ ARG PRIVILEGED_RUNNER="true"
 ARG RUNNER_TAGS="podman-in-podman"
 # Permit running jobs without any tag at all
 ARG RUNNER_UNTAGGED="true"
-ENV REGISTER_NON_INTERACTIVE="true" \
+# Adjust based on usage and storage size to prevent ENOSPACE problems
+ARG CLEAN_INTERVAL="24h"
+ENV CLEAN_INTERVAL="$CLEAN_INTERVAL" \
+    REGISTER_NON_INTERACTIVE="true" \
     RUNNER_TAG_LIST="$RUNNER_TAGS" \
     REGISTER_RUN_UNTAGGED="$RUNNER_UNTAGGED" \
     REGISTER_ACCESS_LEVEL="ref_protected" \