feat(spanner): Add support for Cloud Spanner Default Backup Schedules

PiperOrigin-RevId: 688946300

google/spanner/admin/instance/v1/spanner_instance_admin.proto

@@ -972,6 +972,24 @@ message Instance {
     ENTERPRISE_PLUS = 3;
   }
 
+  // Indicates the default backup behavior for new databases within the
+  // instance.
+  enum DefaultBackupScheduleType {
+    // Not specified.
+    DEFAULT_BACKUP_SCHEDULE_TYPE_UNSPECIFIED = 0;
+
+    // No default backup schedule will be created automatically on creation of a
+    // database within the instance.
+    NONE = 1;
+
+    // A default backup schedule will be created automatically on creation of a
+    // database within the instance. The default backup schedule creates a full
+    // backup every 24 hours and retains the backup for a period of 7 days. Once
+    // created, the default backup schedule can be edited/deleted similar to any
+    // other backup schedule.
+    AUTOMATIC = 2;
+  }
+
   // Required. A unique identifier for the instance, which cannot be changed
   // after the instance is created. Values are of the form
   // `projects/<project>/instances/[a-z][-a-z0-9]*[a-z0-9]`. The final
@@ -1093,6 +1111,18 @@ message Instance {
 
   // Optional. The `Edition` of the current instance.
   Edition edition = 20 [(google.api.field_behavior) = OPTIONAL];
+
+  // Optional. Controls the default backup behavior for new databases within the
+  // instance.
+  //
+  // Note that `AUTOMATIC` is not permitted for free instances, as backups and
+  // backup schedules are not allowed for free instances.
+  //
+  // In the `GetInstance` or `ListInstances` response, if the value of
+  // default_backup_schedule_type is unset or NONE, no default backup
+  // schedule will be created for new databases within the instance.
+  DefaultBackupScheduleType default_backup_schedule_type = 23
+      [(google.api.field_behavior) = OPTIONAL];
 }
 
 // The request for