manifests: Use dracut instead of dracut-core for non-OSTree systems

This patch modifies manifests/packages-elxr.yaml, manifests/packages-elxr.yaml and manifests/packages-orin.yaml to install the dracut package instead of dracut-core on non-OSTree systems.

On non-OSTree systems, the default initramfs generator is initramfs-tools. While dracut-core is installed, it is not used by the system as the default tool.

On OSTree systems, we specify dracut in the manifest. The dracut package is in conflict with initramfs-tools, which is defined in debian/control. Installing dracut on these systems automatically ensures it is used as the default initrd tool.

This change ensures a consistent initramfs generation process across both OSTree and non-OSTree systems where dracut is the preferred tool.