tools: Refactor changelog generation

[Andreea-L]

This PR reworks the generate_debian_changelog.sh. Namely it:

• Adds args for author and email, so we stop tagging every mavsdk dev with Helge's name; when not provided, by default the author is "MAVSDK Team"
• Replaces the previous git describe used for the default tag version with either the current commit hash (+ "0v" prepended) or the tag which points to the commit hash. This is to prevent dpkg-buildpackage errors, since in the cases where a commit is not tagged and its hash does not start with a digit, the deb build fails:

dpkg-buildpackage: error: version number does not start with digit

This meant you basically couldn't reliably issue a build on a non-tagged mavsdk commit.

[JonasVautherin]

Thanks! 🚀

[julianoes]

Amazing, thanks for the PR!