Create teardown function for `App` instance

[jalextowle]

Description

Functions should be created that provide a flow to tear down an API deployment that is created with getAppAsync. "Teardown" in this context means that another App instance and fresh dependencies can be safely deployed without the original App throwing errors or otherwise stopping execution.

Context

This is a very important feature for testing. The architecture of the RFQT tests makes using an in-process App instance essential, but this also means that the app cannot simply be "killed" by killing the process (that would kill all of the tests).