Tests: Add e2e test for image promotion flow

[simonferquel]

Description

One of the promise of the CNAB storage to a registry is that if a CNAB manifest is deeply copied (or mounted) into another repo (on the same or an other registry), it will:

• just work
• override all component images with images coming from the new repo at install time

This is to ensure that if a user has Pull access to a repo where a CNAB lives, he also has sufficient rights to install it by design. (other bonus effects are: security scanning can work at the application level trough manifest crawling, image promotion works at the application level as well).

Test steps:

1. Build a sample Docker-app
2. Push it to a registry
3. Deep-copy the app manifest to another registry
4. Install the app from this new registry
5. Check that all services are referencing digested references coming from the same repo as the app itself.