Add restoreBackup support for sql db instance

[modular-magician]

Fixes #2446

Add support for the very imperative restoreBackup action. This change essentially triggers the restoreBackup action:

1. After the resource is created and restore_backup_context is set
2. At the end of update if restore_backup_context has a change

If this PR is for Terraform, I acknowledge that I have:

• 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).
• Generated Terraform, and ran make test and make lint to ensure it passes unit and linter tests.
• 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).
• Ran relevant acceptance tests (If the acceptance tests do not yet pass or you are unable to run them, please let your reviewer know).
• Read the Release Notes Guide before writing my release note below.

Release Note Template for Downstream PRs (will be copied)

sql: added restore from backup support to `google_sql_database_instance`

Derived from GoogleCloudPlatform/magic-modules#4336

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