[Feature request] Release AppImage

**Is your feature request related to a problem? Please describe.**
Currently only a Debian package and Windows installer are released, other distros are out of luck for installation. Moreover, some people might find it more convenient to run a portable binary that they can delete when not needed anymore.

**Describe the solution you'd like**
Release a prebuilt AppImage.

**Describe alternatives you've considered**
Flatpak might also be favorable for installation on non-Debian distros.

**Additional context**
Some systems employed in corporate or educational environments might not permit system-wide installation, so an AppImage would also solve that.

Inspect the repository's existing Debian package and Windows installer release configuration first, then trace how those artifacts are built and published. Add a prebuilt AppImage to the release process and verify that it can run portably on supported non-Debian systems.

Written by the indexing model from the issue text.