Expose settings.backup_configuration.backup_retention_settings.retained_backups

[aleccool213]

Describe the solution you'd like

I would like to access this setting to increase my retained backup count from the default of 7 days to 90 days.

Describe alternatives you've considered

Not accessible so I cannot use the module.

Additional context

Link to resource docs: https://registry.terraform.io/providers/hashicorp/google/latest/docs/resources/sql_database_instance#retained_backups

Screenshot:

[eak12913]

Closing due to repo sunset