Evaluate generating and releasing archlinux.ipxe

As explained in FS#70767 we lack verification for the IPXE script, that is loaded by the IPXE images, as the script is dynamically generated by archweb.

However, given that e.g. mirror information does not change very frequently, we can evaluate whether we can generate the script (and codesign it the same way we sign the netboot artifacts) in the release pipeline of this repository to close this verification gap and add the script to the release artifacts, that archweb will utilize.