Add deletion_protection field to Secret Manager - Regional Secret

[SamanthaMathews]

Add deletion_protection field to make deletion actions require an explicit intent

Part of https://github.com/hashicorp/terraform-provider-google/issues/18854 Release Note Template for Downstream PRs (will be copied)

See Write release notes for guidance.

secretmanager: added `deletion_protection` field to `regional_secret` to allow setting tags for regional_secrets at creation time

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