Add EncryptionKeyVersion key2027 buffer for FRS KEK rotation

[Brandon (Toritos01)]

Additive enum entry so FRS can reference the 2027 tenant encryption key version one rotation ahead of need (buffer). key2026 already exists.

Companion to FRS scripts/tenantEncryptionKey/keyRotationProcess.md steps 10-12.

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Base commit: 45b18c360a0f8984488d520c398e2bb07896dcb6
Head commit: 2b52dffdc920c0c3c57c051cfa34bac96e01b937

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