Add configuration option to specflow.json whether the generated method is async or sync

[Andras-Csanyi]

Summary: Add configuration option to specflow.json whether the generated method is async or sync

TL;DR; I use specflow for integration testing where I call a bunch of async method. I love that specflow generates the method body for me. What I don't like is that it is a void method instead of async Task, so I always have to rewrite it.

Proposal: Configuration option in specflow.json where I can define what method body I'll get.

[QuentinMM]

Indeed this would be awesome! But I would rather let writing the method template when creating bind classes.