ci: add automatic docker image building

.gitlab/ci/pushAsLatestVersion.sh

@@ -0,0 +1,7 @@
+#!/usr/bin/env sh
+
+# If this is a pipeline of a version tag, also push this version 
+# as latest to the registry alias $2:latest
+if echo -n $1 | grep -Eq 'v[0-9]+\.[0-9]+\.[0-9]+'; then
+  docker push $2:latest;
+fi