Add brightness control support with brightnessctl (#626)

* Added key binds to control brightness

I added keybinds to control brightness with brightnessctl. 

F5 to decrease brightness.
f6 to increase brightness.

* Update src/main.zig

Co-authored-by: ShiningLea <anerruption@disroot.org>

* added proper keybinds and configs for brightness control

* Update src/main.zig

Co-authored-by: ShiningLea <anerruption@disroot.org>

* code improvement and changes

* updated en.ini

---------

Co-authored-by: ShiningLea <anerruption@disroot.org>

res/lang/en.ini

@@ -2,6 +2,7 @@ authenticating = authenticating...
 capslock = capslock
 err_alloc = failed memory allocation
 err_bounds = out-of-bounds index
+err_brightness_change = failed to change brightness
 err_chdir = failed to open home folder
 err_console_dev = failed to access console
 err_dgn_oob = log message