Add Pluton attestation APIs

[nguyenteresaMSFT]

Implementing changes for Pluton attestation support.

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[Copilot]

Pull request overview

This PR adds initial Pluton attestation support to the Azure Security Attestation C++ client library by introducing a new AttestPluton public API and factoring shared TPM/Pluton request/response handling into a common helper.

Changes:

• Added AttestationClient::AttestPluton plus corresponding AttestPlutonOptions and PlutonAttestationResult public types.
• Refactored TPM attestation implementation to use a shared AttestBackend<ResultT> helper for both TPM and Pluton.
• Generalized the TPM payload (de)serializer naming for reuse across TPM and Pluton.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
sdk/attestation/azure-security-attestation/src/private/attestation_deserializers_private.hpp	Renames the TPM serializer struct for shared TPM/Pluton usage.
sdk/attestation/azure-security-attestation/src/private/attestation_deserializers_private.cpp	Updates serializer implementation to match the new shared serializer name.
sdk/attestation/azure-security-attestation/src/attestation_client.cpp	Introduces AttestBackend helper and adds AttestPluton implementation.
sdk/attestation/azure-security-attestation/inc/azure/attestation/attestation_client.hpp	Exposes AttestPluton publicly and declares the private AttestBackend helper.
sdk/attestation/azure-security-attestation/inc/azure/attestation/attestation_client_options.hpp	Adds AttestPlutonOptions.
sdk/attestation/azure-security-attestation/inc/azure/attestation/attestation_client_models.hpp	Adds PlutonAttestationResult.

[LarryOsterman]

I want to confirm: All the default options in the AttestPlutonOptions are going to be ignored by the client? In other words, there is no semantic difference between an option being empty and the options being not present.

Normally options bags are expressed as azure_core::Nullable<AttestPlutonOptions> to make the difference between "no options specified" and "options were specified and these are the values".

I understand that there are no options today but there may be options in the future and making this field non-Nullable constrains the values that can be put in the Options bag.

[nguyenteresaMSFT]

Yes, since this is the same approach used for AttestTpmOptions, I decided to keep this implementation for consistency.