Make the first Event added to a workflow the startup task by default

[Piedone]

Is your feature request related to a problem? Please describe.

You have to select a startup task for a workflow for it to actually work, even if the workflow has a single Event and thus it's obvious that it needs to be the startup task. This is easy to forget and something that we have to specificly teach to people.

Describe the solution you'd like

When adding an Event to the workflow canvas, make it the startup task automatically if there are no other Event-type activities on the canvas yet.

Describe alternatives you've considered

Having a warning notification at the top that you have to select a startup task. This can be complementary, because you could still unset the single Event being a startup task, or you can remove all Events and thus not let the workflow ever run.

[github-actions]

We triaged this issue and set the milestone according to the priority we think is appropriate (see the docs on how we triage and prioritize issues).

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[Piedone]

We're working on this for the Harvest hackathon.

[Piedone]

@durkc will submit a PR for this.