dotAttributes variant that allows specifying GraphvizCommand

[ivan-m]

Currently re-implemented by diagrams-graphviz.

@byorgey I'm tempted to use your dotAttributes' name, but diagrams-graphviz currently imports almost the entire module, so there'll be a name collision. Thoughts?

[byorgey]

Oh, that's not an issue, I would be very happy to drop it from diagrams-graphviz and just import it from graphviz.