feat(sddm): add SDDM theme and config files

system/sddm.conf.d/display.conf

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+[XDisplay]
+# Xsetup script path
+# A script to execute when starting the display server
+DisplayCommand=/etc/sddm/scripts/Xsetup

system/sddm.conf.d/theme.conf

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+[Theme]
+Current=sugar-candy

system/sddm/scripts/Xsetup

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+#!/bin/sh
+
+xrandr \
+  --output DP-0 --mode 1920x1080 --pos 0x0 --rate 144 \
+  --output DP-4 --mode 1920x1080 --pos 1920x0 --rate 270 --primary