[Feature] Add doc for the feature of checkpoint-snapshot align.

### Search before asking

- [X] I searched in the [issues](https://github.com/apache/incubator-paimon/issues) and found nothing similar.

### Motivation

After #1486 is implemented, we need to add documentation to explain this feature.

### Solution

_No response_

### Anything else?

_No response_

### Are you willing to submit a PR?

- [X] I'm willing to submit a PR!

Read issue #1486 first to understand the checkpoint-snapshot align feature and confirm that its implementation is complete. Then find the project's documentation structure and add an explanation of the feature, with the work done when users can understand what it does and how to use it.

Written by the indexing model from the issue text.