Create network installer artifacts (HTTP boot) during the compose process

[mmartinv]

Based on #24 we need to provide the network installer artifacts for things like PXE boot or HTTP boot: Note the missing os directory in Fedora 40 vs Fedora 39.

Goal

• Create new image type for the Anaconda Network Installer to provide the missing artifacts.
• The new image type should generate, if possible, a size optimized installer image that might require a new stage in osbuild to allow the removal of files within the resulting tree (Please see: Anaconda installer images size on osbuild generated images. osbuild/images#409) .

Acceptance Criteria

• It's possible to generate the missing artifacts with the new osbuild image type.
• The documentation is updated accordingly.
• The new artifact have its corresponding CI tests.