Changelog API allow to define version header format
See discussion: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/144738#note_1797069988
### Problem
We provide an API to generate the changelogs ([see documentation](https://docs.gitlab.com/ee/user/project/changelogs.html), [api docs](https://docs.gitlab.com/ee/api/repositories.html#add-changelog-data-to-a-changelog-file)).
But it's not possible to define the format of changelog headers. It's hardcoded to ensure that the versions order is consistent
```
16.9.1
...
16.9.0
....
```
<img src="/uploads/9704daa142035558c60c21ff178c6b75/Screenshot_2024-03-01_at_14.00.36.png" width=300px>
[see code](https://gitlab.com/gitlab-org/gitlab/blob/88aa9c12af1e237971efad91ea894fcb6aa709e2/lib/gitlab/changelog/release.rb#L74-77)
### Proposal
Add an option to configure headers. For example, to include `v` at the beginning.
<img src="/uploads/bf84104ec31ad0573389473a6234369e/Screenshot_2024-03-01_at_14.03.59.png" width=300px>
issue