feat: :warning: reduce images size and stop bundling sources (#5721)

feat: reduce images size and stop bundling sources

Do not copy sources anymore, and reduce packages of the base images by
not using builder images.

If needed to rebuild, just build the container image from scratch by
following the docs. We will slowly try to migrate all backends to the
gallery to keep the core small.

This PR is a breaking change, it also sets the base folders to /models
and /backends instead of /build/models and /build/backends.

Signed-off-by: Ettore Di Giacinto <mudler@localai.io>
Signed-off-by: Ettore Di Giacinto <mudler@users.noreply.github.com>