udev: use a more secure flashlight rule

Replace the chmod 666 udev rule by a more secure one, using chgrp.
Inspired by Volla Yggdrasil udev rules [1].

[1]: https://gitlab.com/ubports/porting/reference-device-ports/android10/volla-phone-x/volla-yggdrasilx/-/blob/focal/overlay/system/usr/lib/udev/rules.d/70-yggdrasilx.rules?ref_type=heads#L156

overlay/system/lib/udev/rules.d/70-surya.rules

@@ -237,4 +237,6 @@ ACTION=="add", KERNEL=="block/platform/soc/4804000.ufshc/by-name/frp", OWNER="sy
 ACTION=="add", KERNEL=="block/platform/soc/8804000.sdhci/by-name/frp", OWNER="system", GROUP="system", MODE="0600"
 ACTION=="add", KERNEL=="kmsg", OWNER="root", GROUP="system", MODE="0620"
 ACTION=="add", KERNEL=="msm_npu", OWNER="system", GROUP="system", MODE="0644"
-ACTION=="add", KERNEL=="flashlight", SUBSYSTEM=="leds", RUN+="/usr/bin/chmod 666 /sys/class/leds/flashlight/brightness"
+
+# Set flashlight permissions so indicator-power can access it
+ACTION=="add|change", SUBSYSTEM=="leds", KERNEL=="flashlight", RUN+="/bin/chgrp android_media /sys/class/leds/%k/brightness"