Validate the target VM name and ensure uniqueness

[mansam]

Validates the format of the targetVMName or the source VM name if the target name was not provided. Also ensures that there is not already a VirtualMachine in the namespace with that name.

Removing the normalization can be a follow up, but it should be harmless for now since any names that would be normalized should be caught by the validation.

Fixes https://bugzilla.redhat.com/show_bug.cgi?id=1894825

[kubevirt-bot]

@mansam: Adding the "do-not-merge/release-note-label-needed" label because no release-note block was detected, please follow our release note process to remove it.

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[kubevirt-bot]

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This pull-request has been approved by: fdupont-redhat, mansam
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