[RFE] Enable multi-arch deployments

[dtantsur]

With IPA downloader gaining support for different architectures, we can now download kernel/ramdisk for x86_64 and aarch64, at least when network boot is not involved.

There are quite a few questions to resolve first:

1. Should this feature be opt-in? Downloading one more set of kernel/ramdisk pairs is time-consuming.
2. How do we detect the default architecture? Currently, we only correctly configure x86_64.
3. Download the aarch64 images from tarballs.opendev.org or from our cache?
4. Any changes needed to enable network boot? Do we disallow dhcp to be set when this is enabled?

/kind feature

[Rozzii]

/triage accepted

[Rozzii]

We have agreed to elevate this discussion, this will be discussed as part of the Metal3 Team Meetup and also will have a working group that should sort out IPA hosting, maintenance and formats related issues.

[metal3-io-bot]

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/lifecycle stale

[dtantsur]

/remove-lifecycle stale
/lifecycle frozen