feat(tazjin/dotfiles): add waybar configuration

This configuration is not automatically placed anywhere yet, because I'm also
still actively iterating on it.

Change-Id: I0a13fcbc2b9a5587480f6a69a73ab99b36d209e6
Reviewed-on: https://cl.tvl.fyi/c/depot/+/12435
Tested-by: BuildkiteCI
Reviewed-by: tazjin <tazjin@tvl.su>
Autosubmit: tazjin <tazjin@tvl.su>

users/tazjin/dotfiles/default.nix

@@ -1,4 +1,5 @@
 _: {
   dunstrc = ./dunstrc;
   niri = ./niri.config.kdl;
+  waybar = ./waybar;
 }