(pipelines): Pass changeset validation automatically if there's no changes or no changeset created

### Description

I have implemented Changeset validation according https://github.com/aws/aws-cdk/blob/master/packages/@aws-cdk/pipelines/README.md#validation to our pipeline.

It would be nice that this validation passes automatically if there's no changeset created (changes in commit only to pipeline itself, or just rerun for some other reason).

### Use Case

Speed up release by removing need to approve no changes on each environment.

### Proposed Solution

It could work like `ConfirmPermissionsBroadening` by approving automatically if no changeset exists.

Maybe it could be even own class offering also notification possibility like `ConfirmPermissionsBroadening` does.

### Other information

_No response_

### Acknowledge

- [X] I may be able to implement this feature request
- [X] This feature might incur a breaking change

Start with the Changeset validation section in packages/@aws-cdk/pipelines/README.md and inspect the implementation and usage of ConfirmPermissionsBroadening. Define the no-changeset behavior and verify that pipeline executions with no changes or no changeset complete without manual approval, while preserving the existing approval path when changes are present.

Written by the indexing model from the issue text.