Unblock EXTERNAL/EXTERNAL_VPC Cloud KMS key creation.

[modular-magician]

The external_protection_level_options field had been nested within the attestation field by accident. See hashicorp/terraform-provider-google#15004 for more information about this change..

NOTE: this is the initial deprecation notice, and we are just adding a duplicate set of fields outside of attestation. When the old field is eventually removed, it should not break any CUJs because the current state of things does not allow for successful key creation (malformed requests would be rejected by the server). The old, deprecated field will be removed in the next release.

Release Note Template for Downstream PRs (will be copied)

kms: added top-level `external_protection_level_options` field in `google_kms_crypto_key_version` resource

kms: `attestation.external_protection_level_options` has been deprecated in favor of `external_protection_level_options` in `google_kms_crypto_key_version` 

kms: added `crypto_key_backend` field to `google_kms_crypto_key` resource

Derived from GoogleCloudPlatform/magic-modules#9931

[conventional-commit-lint-gcf]

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