changelog: create links in release headlines for past releases

[tiborsimko]

The release process has become recently more automatised by means of using the conventional commits and the Release Please.

This has led to the new formatting of release notes in CHANGELOG.md files for REANA components.

Whilst the old release notes were well ported, the release headlines themselves do not contain links to GitHub details.

For example, take reana-commons, and compare:

## [0.9.8](https://github.com/reanahub/reana-commons/compare/0.9.7...0.9.8) (2024-03-01)

with older release:

## 0.9.5 (2023-12-15)

The goal of this issue is to update all REANA repositories's CHANGELOG.md files in order to use the former style, i.e. basically to expand the ## lines to also include the GitHub "compare" link.