Add Undo and Redo to Hotkeys

[Supinic]

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

In Chatterino, the keyboard shortcuts for actions Undo and Redo are bound to CTRL+Z and CTRL+SHIFT+Z respectively, without the ability to change this in the Hotkeys tab. They're possibly taken from the Qt widget.

I would like if these were added to the Hotkeys tab, so that they can be rebound per user preference.

Screenshots

No response

OS and Chatterino Version

Chatterino 2.5.4 (commit 117d06b92) built with Qt 6.10.1 (running on 6.10.2)
Running on KDE Flatpak runtime, kernel: 6.18.10-200.fc43.x86_64, running from Flatpak