docs(s3): correct heading levels Object Ownership / Bucket deletion (#…

…16790)

In the README file, the chapters `Object Ownership` and `Bucket deletion` are created as subchapter of `The URL for objects`. In my opinion they do not have a relationship to `The URL for objects`. Probably this hierarchy was created by mistake.

I would suggest to move chapters `Object Ownership` and `Bucket deletion` to the same hierarchy level than `The URL for objects`.

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*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

packages/@aws-cdk/aws-s3/README.md

@@ -402,13 +402,13 @@ bucket.virtualHostedUrlForObject('objectname'); // Virtual Hosted-Style URL
 bucket.virtualHostedUrlForObject('objectname', { regional: false }); // Virtual Hosted-Style URL but non-regional
 ```
 
-### Object Ownership
+## Object Ownership
 
 You can use the two following properties to specify the bucket [object Ownership].
 
 [object Ownership]: https://docs.aws.amazon.com/AmazonS3/latest/dev/about-object-ownership.html
 
-#### Object writer
+### Object writer
 
 The Uploading account will own the object.
 
@@ -418,7 +418,7 @@ new s3.Bucket(this, 'MyBucket', {
 });
 ```
 
-#### Bucket owner preferred
+### Bucket owner preferred
 
 The bucket owner will own the object if the object is uploaded with the bucket-owner-full-control canned ACL. Without this setting and canned ACL, the object is uploaded and remains owned by the uploading account.
 
@@ -428,7 +428,7 @@ new s3.Bucket(this, 'MyBucket', {
 });
 ```
 
-### Bucket deletion
+## Bucket deletion
 
 When a bucket is removed from a stack (or the stack is deleted), the S3
 bucket will be removed according to its removal policy (which by default will