add TAG_SUFFIX arg to lighthouse build

intended to avoid sporadic failures when running lcli on github CI runners, likely related to
non-portable builds

app/data/container-build/cerc-lighthouse/Dockerfile

@@ -1,4 +1,5 @@
-FROM sigp/lighthouse:v4.1.0-modern
+ARG TAG_SUFFIX="-modern"
+FROM sigp/lighthouse:v4.1.0${TAG_SUFFIX}
 
 RUN apt-get update; apt-get install bash netcat curl less jq -y;