feat(google_cloudsql_postgres): allow configuring backup start time

[stevejalim]

Adds an optional backup_start_time variable (HH:MM, UTC) that maps to the backup_configuration.start_time argument on the primary instance.

Defaults to null, matching prior behavior where Cloud SQL picks a random start time, so this is a no-op for existing callers.

[github-actions]

Release plan

Directory	Previous version	New version
google_cloudsql_postgres	0.9.0	0.10.0

[stevejalim]

Thanks for the r+ @bqbn -- do you know if this can just be merged or if it need any kind of extra process (atlantis, for instance)?

[Copilot]

🟡 Changes recommended

The new backup_start_time input lacks validation for the documented HH:MM UTC format, which can lead to avoidable apply-time/provider errors.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Pull request overview

Adds a new optional module input to control the Cloud SQL automated backup window start time for the primary instance, while preserving existing behavior when unset.

Changes:

• Introduces backup_start_time input (defaults to null) in variables.tf.
• Wires backup_start_time through to settings.backup_configuration.start_time on the primary Cloud SQL instance.
• Documents the new input in the module README.

File summaries

File	Description
google_cloudsql_postgres/variables.tf	Adds new backup_start_time variable (nullable string) for backup window configuration.
google_cloudsql_postgres/main.tf	Sets backup_configuration.start_time from the new variable.
google_cloudsql_postgres/README.md	Adds the new input to the documented inputs table.

Review details

• Files reviewed: 3/3 changed files
• Comments generated: 1
• Review effort level: Lite

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