Single app build for testing

[Zasa-san]

Research and, if possible, implement a single step in the CI pipeline that does the app build and setup. The goal is to avoid every e2e job having to build the app on every run. Instead, e2e workflows should use the same app build to save time.

Also:

• check if the same can be done for external services, mongo and elastic
• check if there's a way that the build step produces something that could be used later for other purposes (like using that build to fast deploy it into staging for testing)