Adds Maltroach bar sign! (#79532)

## About The Pull Request
Accepted submission for the bar sign contest! It was really fun, thank
you!
Changes barsigns.dm to include information for the sign, and
barsigns.dmi to include the maltroach sign itself as well as a simple
light mask!

## Why It's Good For The Game
Mothroaches are cute and fluffy!


![RoachSign](https://github.com/tgstation/tgstation/assets/143907841/c06dcab2-eed5-45a9-8de8-7feed7dc11e4)

## Changelog
🆑
add: Maltroach bar sign!
/🆑

Co-authored-by: moth <MothLove@protonmail.com>

code/game/machinery/barsigns.dm

@@ -388,6 +388,12 @@ MAPPING_DIRECTIONAL_HELPERS(/obj/machinery/barsign, 32)
 	desc = "Drink till you puke and/or break the laws of reality!"
 	neon_color = "#00cc33"
 
+/datum/barsign/maltroach
+	name = "Maltroach"
+	icon = "maltroach"
+	desc = "Mothroaches politely greet you into the bar, or are they greeting eachother?"
+	neon_color = "#649e8a"
+
 // Hidden signs list below this point
 
 /datum/barsign/hiddensigns