For a gmail add-on we are developing we need to be able to put different API url's for development vs. production, along with some other configurations. What would be the proper place to put these configurations and how to read them? I saw we can add script properties from Project Properties window and i am guessing we can read them using PropertiesService, but the problem is how can we have different configurations based on environment.
Any ideas?
As you said, store them in the Properties Service, specifically, the Script Properties. You can still access them and modify them after you publish.