Unify the scaffolding!

[gauron99]

We have made a few immediate fixes for parts of scaffolding which were necessary at the time. Now that we are past that, we can unify and cleanup the scaffolding code.

This issue covers *ALL of the scaffolding unification. This might be broken down into multiple PRs.
related work items:

• go scaffolding with buildpacks
• python injectors
• remote deployments

related #3005

/assign