Add Ubuntu server workload

[0xFelix]

What this PR does / why we need it:

Add Ubuntu server workload

Only server workloads have cloud images, this allows to display import urls after #406 is merged.

Release note:

Add Ubuntu server workload

[kubevirt-bot]

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[openshift-ci]

Hi @0xFelix. Thanks for your PR.

I'm waiting for a kubevirt member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

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[0xFelix]

See #412