Support horziontal diagram in activity-diagram-beta new syntax.

Is your feature request related to a problem? Please describe. The old syntax of activity diagram can set arrow direction, so I can draw the diagram in horizontal direction. I mean the whole diagram, not only elseif.

Describe the solution you'd like Add support arrow direction setting in new syntax just like old syntax.

Additional context The output I want in activity diagram new syntax, this image is written in plantuml activity diagram old syntax: