Set architecture to amd64 across all templates

[lyarwood]

/cc @0xFelix /cc @ksimon1

What this PR does / why we need it:

The current set of templates are only verified on amd64 so to avoid users attempting to run them on aarch64 etc set the architecture within the VirtualMachineInstanceSpec.

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged): Fixes #

Special notes for your reviewer:

Release note:

The architecture of each `VirtualMachine` is now  set to `amd64` within the `VirtualMachineInstanceSpec`.

[ksimon1]

Probably related thread https://groups.google.com/g/kubevirt-dev/c/Fiz0g8cm2_g/m/pFcOAEczAQAJ?utm_medium=email&utm_source=footer

[lyarwood]

/retest-required

[fabiand]

Related to this I still wonder why architecture is a field on the VM spec.

See https://groups.google.com/g/kubevirt-dev/c/Fiz0g8cm2_g And https://github.com/kubevirt/kubevirt/pull/8293#issuecomment-2043288058

[lyarwood]

/retest-required

[kubevirt-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: 0xFelix

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[ksimon1]

/lgtm