Provide prebuilt images for localinstall

[pawiecz]

Currently localinstall provides a way to build all the Maestro components from scratch. Although it's great for educational purposes, some use-cases might depend only on interacting with Maestro instance (without the infrastructure setup step).

In order to do so (and to make it available quickly), localinstall could use prebuilt images (including cached kernel sources) unless forced to rebuild the whole setup from scratch.

An example of this behavior is available in lava/pkg/docker-compose (see .env):

• prebuilts are used by default
• user can provide specific image/tag
• rebuild from scratch can be requested demand