chore: deploy app to new infra (#13286)

This PR changes the app to deploy to builds.opentrons.com instead of the
legacy bucket.

It also refactors the app build workflow in some ways that should make
it a little more pleasant to deal with:
- Separate backend tests from builds
- Reduce duplication between internal release and release builds
- Make the logic about what kind of build we have clearer

Author: sfoster1