api: recognize Fabric GPU sharing strategy in validation

[AkshatDudeja77]

What this PR does

• Allows the API validation layer to recognize the Fabric GPU sharing strategy
• Prevents false validation errors when Fabric-backed GPUs are configured
• Keeps behavior fully gated behind existing feature gates

Why this is needed

Fabric-attached GPUs (IMEX / NVLink fabric) introduce sharing modes that are not purely local.
Without this change, valid Fabric configurations are rejected during validation.

This PR is intentionally minimal and scoped to validation only.

Scope

• Validation logic only
• No behavior change unless the corresponding feature gates are enabled

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