Merge several Geo Time Series™ together.
MERGE function expects a LIST of Geo Time Series™ on the top of the stack. It will consume these GTS and push onto the stack a single GTS instance
with all measurements found in the GTS instances present in the LIST. The name and labels of the resulting GTS instance are those of the first one of the
MERGE do not override values on the same timestamp, they are appenned.