GH-7311 - Increasing deletion timeout wait

- Per our discussion around the PR to increase this initially, we
weren't sure if 1 minute would be sufficient.  Well, it turns out it
wasn't for me today (we don't delete these often so not sure how
often people run into this).

Picking another somewhat arbitrary value of 5 minutes in the hopes
that it will be sufficient (today it took a little over 2 minutes).

builtin/providers/aws/resource_aws_db_option_group.go

@@ -280,7 +280,7 @@ func resourceAwsDbOptionGroupDelete(d *schema.ResourceData, meta interface{}) er
 	}
 
 	log.Printf("[DEBUG] Delete DB Option Group: %#v", deleteOpts)
-	ret := resource.Retry(1*time.Minute, func() *resource.RetryError {
+	ret := resource.Retry(5*time.Minute, func() *resource.RetryError {
 		_, err := rdsconn.DeleteOptionGroup(deleteOpts)
 		if err != nil {
 			if awsErr, ok := err.(awserr.Error); ok {