Provide AppImage from Ubuntu 22.04

[Nerixyz]

Checklist

• I'm reporting a problem with Chatterino
• I've verified that I'm running the most recent nightly build or stable release
• I've looked for my problem on the wiki
• I've searched the issues and pull requests for similar looking reports

Describe your issue

The currently provided AppImage is from Ubuntu 20.04 with Qt 5.12.12 (#4400). This Qt version is EOL and contains bugs visible in Chatterino today (e.g. trails in animated emotes). An AppImage that is built against Qt 5.15 would be really nice (especially for the 7TV fork: SevenTV#215).

If I understand AppImages correctly, then once this is provided, support for Qt 5.12 can be dropped since AppImages bundle the Qt dependency (#4292) and users on Ubuntu 20.04 can use the AppImage.

Screenshots

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OS and Chatterino Version