Add a janitorial 'borg plunger (#85475)

## About The Pull Request
I got annoyed at not being able to plung vents when there's a clog. This
PR corrects that. I copied all of the cyborg mop attributes to make
this. This is my first PR on this server, but I did test it on a local
server, and it indeed, plungs.

## Why It's Good For The Game
More content for janitorial cyborg. They really should have a plunger,
to be honest. It just makes sense to me.

## Changelog
🆑
add: Added a cyborg plunger for janitorial modules
/🆑

code/game/objects/items/robot/robot_upgrades.dm

@@ -208,6 +208,16 @@
 
 	items_to_add = list(/obj/item/cautery/prt)
 
+/obj/item/borg/upgrade/plunger
+	name = "janitor cyborg plunging tool"
+	desc = "An integrated cyborg retractable plunger. It's meant for plunging things, duh."
+	icon_state = "module_janitor"
+	require_model = TRUE
+	model_type = list(/obj/item/robot_model/janitor)
+	model_flags = BORG_MODEL_JANITOR
+
+	items_to_add = list(/obj/item/plunger/cyborg)
+
 /obj/item/borg/upgrade/syndicate
 	name = "illegal equipment module"
 	desc = "Unlocks the hidden, deadlier functions of a cyborg."