IllumiDesk submission type option

[hoffm386]

In DS, the process for making a lab available for students to open in IllumiDesk (after adding the assignment to Canvas with this gem) is currently:

1. Change the submission type to "External Tool"
2. Search for "illumidesk" in the text box then select the IllumiDesk URL from the drop-down
   • Honestly I don't know why this step is required, but everything breaks if you don't do it. The assignment becomes impossible to open if you skip this step
3. Go to this generator tool made by a former instructor. It just interpolates the right strings to make the relevant URL, which is displayed at the bottom
   • Waiting for the Heroku dyno to spin up is annoying
   • It is not sustainable long-term for this to stay on a former instructor's Heroku account
4. Replace the IllumiDesk URL in the text box with the one generated from that Heroku app

I propose that we set up this gem to do those steps instead

This seems potentially challenging to implement via an API interface because I don't understand what step 2 is doing under the hood. We may find that programmatically setting the external tool URL just doesn't work. So then maybe a good alternative would be for the gem to print out the appropriate URL, to save a step and avoid depending on that Heroku app