feat(pkgs/Profpatsch/alacritty): init dark mode dbus daemon

A simple dbus daemon that writes the alacritty config to
`~/.config/alacritty/alacritty-colors-autogen.toml` on startup and
whenever a change between dark/light mode is requested.

Alacritty only implements an config file isync watcher, no SIGHUP
handler or similar, so we have to actually write the config file lol.

This is all a little glue-y, but idk, whatever.

Further reading & inspo:

https://github.com/alacritty/alacritty/issues/5999
https://www.christianfosli.com/posts/2024-on-colorscheme-changed/
https://github.com/christianfosli/on-colorscheme-changed

Change-Id: Iac4eb9d85679dc87e28e57d68384645b3b91d08a
Reviewed-on: https://cl.tvl.fyi/c/depot/+/12870
Tested-by: BuildkiteCI
Reviewed-by: Profpatsch <mail@profpatsch.de>

users/Profpatsch/nix-home/default.nix

@@ -186,7 +186,7 @@ let
           ([
             {
               name = "bin/terminal-emulator";
-              path = depot.users.Profpatsch.alacritty;
+              path = depot.users.Profpatsch.alacritty.alacritty;
             }
           ]);