ci: add automatic docker image building

.gitlab/ci/getRegistryTag.sh

@@ -0,0 +1,8 @@
+#!/usr/bin/env sh
+
+# script returns semantical versioning string linke 2.0.0 (if $1 is v2.0.0) or $1
+if echo -n $1 | grep -Eq 'v[0-9]+\.[0-9]+\.[0-9]+'; then 
+  echo $(echo -n "$1" | cut -c 2-);
+else 
+  echo $1;
+fi