[FEATURE] Enable custom resume requests

**Is your feature request related to a problem? Please describe.**
Based on the just announced pause/suspend features, I asked on Slack what it looked like when you resume a workflow. Danny shared this picture:


While this works, I can see folks needing nicer UI/messages/etc for workflows managed by non-technical people. So perhaps allow a way for us to say, "use this url on resume", so we can present something nicer. Or, at minimum, perhaps let us use a string value for that message, one where I could use a bit of HTML, etc, to generate a user-friendly message.

**Describe the solution you'd like**
Oops, did that above.

**Do you have a workaround?**
Nope.