It seems that you are mainly interested in how to build preview environments for your app, these posts describe an approach to get there:
- https://softwaremill.com/preview-environment-for-code-review...
- https://softwaremill.com/preview-environment-for-code-review...
- https://softwaremill.com/preview-environment-for-code-review...
While the examples use Gitlab, it shouldn't be very hard to port the same idea to a Bitbucket.