Use GitHub usernames in changelogs for releases

[CasperWA]

Closes #102

Updates CD - Release to use the github-changelog-generator directly from the public Docker image, instead of the GitHub Actions CharMixer/auto-changelog-action, which essentially proxies usage of that same Docker image.
The reason for this switch is the need to use the --usernames-as-github-logins option, which is not supported by the proxy action. The action is quite static in terms of the supported options and does not allow one to add miscellaneous options.
Instead, since GitHub Actions supports using public Docker images straight up as a step, this is done, passing in the options to the generator tool via the args input. It's a bit more opaque concerning the options passed to the generator tool now, however, the freedom to use whichever option we want is apparent.

In order to parse the options correctly, a pre-parsing step has been introduced to the workflow.

Indeed, to completely remove the Action from this repository seemed to be the most straight-forward thing to do, hence this switch has also been implemented for the CI/CD - New updates to default branch workflow, which creates a temporary changelog with unreleased changes for the latest "version" in the documentation.

Finally, the --usernames-as-github-logins option is added to the changelog generation, which is then appended to the release description, making all named contributions into GitHub handles (instead of markdown links). This will auto-add "contributors" on the GitHub page of the release.

Markdown links are kept for other generated changelogs, since these are mainly shown in the documentation, which needs these named references to be full links.

[codecov]

Codecov Report

Merging #115 (9bb7f57) into main (20bf35a) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #115   +/-   ##
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  Coverage   65.67%   65.67%           
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  Files           9        9           
  Lines         472      472           
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  Hits          310      310           
  Misses        162      162           

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