/kind feature

Describe the solution you'd like
Apart from enabling/disabling confidential computing, GCP allows determining the confidential instance type (sev/sev-snp/tdx) see the docs.
As a user, I'd like to specify the type of confidential computing technology backing the confidential nodes provisioned in a cluster.

Anything else you would like to add:
[Miscellaneous information that will assist in solving the issue.]
compute API behavior:

• Setting the compute ConfidentialInstanceConfig's EnableConfidentialCompute field to True will set the type to SEV on machines that support it (backward compatibility). (I'm not sure about c3d machines, I have to test that yet).
• Setting EnableConfidentialCompute=True on any machine type that supports other technology that isn't SEV (tdx for example) will raise an error.
• Setting any supported value to ConfidentialInstanceType in ConfidentialInstanceConfig will override EnableConfidentialCompute=False, and will instead provision a confidential VM of the specified type.