Determine which modules should be enabled with user-provided kickstart blobs

[achilleas-k]

#631 (comment)

• We don't want to parse user blobs.
• We want users to be able to do things like add users, which requires a module that we generally enable conditionally.
• Do we also want users to be able to make an unattended/automatic ISO without needing to specify everything? That would require module control.