Build speed: Install/preview-docker

[mads-hartmann]

The component install/preview gets rebuild on every build because it has an argdeps dependency on version. This dependency is needed, which means that for now, we can't avoid having the component be rebuild with every build.

However, we can make it optional to build the component. install/preview:docker isn't needed on all branches, so we could hide it behind a "with-preview-docker" Werft attribute.

Being able to dynamically decide if a component should be build or not depends on a new feature in Leeway (gitpod-io/leeway#95)

[mads-hartmann]

Quick note from chat with Chris

See docs at https://github.com/gitpod-io/leeway#dynaimc-package-scripts. There is no release yet, create a release by creating a tag v.0.2.21 then a GH action will run and produce the release

[mads-hartmann]

✅ Leeway release created here