Replace kwriteconfig5 with a custom tool

[pjones]

The kwriteconfig5 tool is how we currently update settings in KDE configuration files. However:

1. It can only update one setting at a time. Trying to update a bunch of settings is slow.

2. Some settings (e.g., khotkeysrc) use section numbers and therefore we need some way to remove old sections.

We probably need a custom tool written in C++ that can merge entire files as once. Probably from a JSON source which Nix can generate.

[pjones]

If anyone is interested in helping, I have a branch of kconfig that allows us to edit KDE config files with a single command, instead of having to use kwriteconfig.

There's a branch of this repo that brings in my custom kconfig in the flake.nix. However, I haven't made any of the necessary changes to actually switch to kconfig.

[nazarewk]

Looking through the docs we could simply manage own directory (adding/prepending it to $KDEDIRS) with configuration files render through Nix without any external tool?

• https://userbase.kde.org/KDE_System_Administration/Configuration_Files
• https://userbase.kde.org/KDE_System_Administration/KDE_Filesystem_Hierarchy

[toast003]

We have had our own tool for this since #39