Added support for CMEK in alloydb cluster and automated backup

[modular-magician]

Added support for CMEK in alloydb cluster and automated backup.

CMEK is immutable for cluster but it is updatable for automated backup.

This is one of the 2 PR is to fix #13250

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• Searched through the issue tracker for an open issue that this either resolves or contributes to, commented on it to claim it, and written "fixes {url}" or "part of {url}" in this PR description. If there were no relevant open issues, I opened one and commented that I would like to work on it (not necessary for very small changes).
• Ensured that all new fields I added that can be set by a user appear in at least one example (for generated resources) or third_party test (for handwritten resources or update tests).
• Generated Terraform providers, and ran make test and make lint in the generated providers to ensure it passes unit and linter tests.
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• Read the Release Notes Guide before writing my release note below.

alloydb: added `encryption_config` and `encryption_info` fields in `google_alloydb_cluster`, to allow CMEK encryption of the cluster's data.

alloydb: added the `encryption_config` field inside the `automated_backup_policy` block in`google_alloydb_cluster`, to allow CMEK encryption of automated backups.

Derived from GoogleCloudPlatform/magic-modules#7781

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