Add Image/Package Mode feature to os_vendor

[kdvalin]

This PR adds the ability to simply specify os_vendor: rhel:mode=image to work with bootc images.

Presently all this does is enable --no_packages automatically since you cannot install packages in bootc/image mode.

[kdvalin]

Trying a smoke test using a FIO bootc image, currently hitting this

TASK [existing_uploads_dir : Make the uploads directory] ***********************
fatal: [192.168.122.143]: FAILED! => {"changed": false, "msg": "There was an issue creating /sysroot/uploads as requested: [Errno 30] Read-only file system: b'/sysroot/uploads'", "path": "/sysroot/uploads"}

This'll be fun

[kdvalin]

Updating the kit_upload_directory to be within /root fixed that problem, will fix it tomorrow.