Preview CHANGELOG in PR

**Is your feature request related to a problem? Please describe.**

I'd like to see a preview of what the CHANGELOG generated from commits will look like.

**Describe the solution you'd like**

Much like the pre-release (canary) section that `@auto-it` adds to the body of a PR. It would be neat if there would be a preview of the CHANGELOG too. That'll make it easy to spot errors or "review" the changelog :)

Example of current pre-release functionality:
```md

📦 Published PR as canary version: Canary Versions
...

```

Something like this would be welcome:
```md

📖 CHANGELOG
...

```

**Describe alternatives you've considered**

none

**Additional context**

none