need to keep it exact same as in TiKV ENCRYPTION_VENDOR_NAME_AWS_KMS.

need to keep it exactly same as TiKV STORAGE_VENDOR_NAME_GCP in TiKV.

PlainKey is used to mark a byte slice as a plaintext key.

Provider is an interface for key management service providers implement encrypt data key in future if needed.

CryptographyType represents different cryptography methods.

EncryptedKey is used to mark data as an encrypted key.