(🎁) Support a summary section

[KotlinIsland]

Is your feature request related to a problem? Please describe.
Yes, I'm converting a project to use the changelog plugin, but their changelog contains a summary section for each version, some of which is very touching and would be a crime to not be able to include.

      <p>0.4.4</p>
      <p>This release is dedicated to the memory of our cat <b>Luna</b>, who passed away due to cancer last year.</p>
      <p>She was kind, smart and loyal. Best cat in the world.</p>
      <p><b>We miss you, girl.</b></p>

Describe the solution you'd like
If the plugin supported an optional 'summary' field that came before the groups.

## [1.2.3]
This version is very good and we would like to thank all the contributers
### Additions
- some addition

Describe alternatives you've considered
Put the summary into a separate section, works okay, but looks a little janky

Additional context
Add any other context or screenshots about the feature request here.