(s3): remove warnings about Object Lock on existing buckets

### Describe the issue

There are a lot of warnings in the CDK documentation about enabling Object Lock on existing buckets.

It's in the README https://github.com/aws/aws-cdk/blob/c979d6bd88f5a0c70611e0302cb6a089d0f11601/packages/aws-cdk-lib/aws-s3/README.md#L720-L723

And in the in-code comments

https://github.com/aws/aws-cdk/blob/c979d6bd88f5a0c70611e0302cb6a089d0f11601/packages/aws-cdk-lib/aws-s3/lib/bucket.ts#L1485-L1507

### Links

It looks like, as of Nov 20, 2023, you can now enable this on existing buckets: https://aws.amazon.com/about-aws/whats-new/2023/11/amazon-s3-enabling-object-lock-buckets/

Read the Object Lock warning in packages/aws-cdk-lib/aws-s3/README.md around lines 720-723 and the related comments in packages/aws-cdk-lib/aws-s3/lib/bucket.ts around lines 1485-1507. Verify the linked AWS announcement applies to existing buckets, then update both locations so they no longer describe enabling Object Lock as unsupported.

Written by the indexing model from the issue text.