* variant: move into internal/attestation
* attesation: move aws attesation into subfolder nitrotpm
* config: add aws-sev-snp variant
* cli: add tf option to enable AWS SNP
For now the implementations in aws/nitrotpm and aws/snp
are identical. They both contain the aws/nitrotpm impl.
A separate commit will add the actual attestation logic.
* Replace external KMS backend logic for AWS, Azure, and GCP with go-kms-wrapping
* Move kms client setup config into its own package for easier parsing
* Update kms integration flag naming
* Error if nil storage is passed to external KMS
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Signed-off-by: Daniel Weiße <dw@edgeless.systems>
