Add staging environment to pipeline

[ericrallen]

Right now testing and releasing is rough because I made the rookie mistake of doing all the dev inside our Slack Workspace.

Now that this has become an actual thing that people use, we need to set up a staging app and add it to the Heroku pipeline and connect it to the develop branch (which also needs to be created).

This should make it easier to test new fixes without impacting our existing users.