Additional custom description for Releases

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

Before I release a project, I like to include some written text with the release in order to better describe especially major changes (see an example [here](https://github.com/ethersphere/bee-js/releases/tag/v3.2.0)). For that, I edit the release-please's comment on the PR which works nicely as release-please then use this text to create the actual GitHub's Release notes. There are two caveats though:

1. I have to manually sync these changes with a commit to `CHANGELOG`
2. If I don't do this as the last step before the release and some new commit lands into it, release-please override these changes in this comment and I have to fish in the edit history for it.

**Describe the solution you'd like**
I would like to add a section into the release-please PR comment marked with comments that would be persisted across the PR's comment updates. For example:
```

This block will be persisted across PR's comment update.

```

Also, GitHub supports [`issue_comment`](https://docs.github.com/en/actions/using-workflows/events-that-trigger-workflows#issue_comment) that allows tracking of updated comments. So the user of for example the Release Please Github Actions could trigger release-please also on updated comment. So the Release Please could have another "category of action" for this type of event to update `CHANGELOG` with updated comment.

**Describe alternatives you've considered**
There are manual workaround but they are more and more annoying to me.