Adds flare packs to FTL vendors (#7118)

# About the pull request

Adds signal flare packs to the FTL vendors for 5 points a pack. 

# Explain why it's good for the game

FTL is a role that's based around leadership and calling fire support,
in practice. It seems silly they don't have the option to buy more
signal flares to do this with.

# Testing Photographs and Procedure
Booted the game, signal flare packs in vendor, each costs 5 points. 
<details>
<summary>Screenshots & Videos</summary>

Put screenshots and videos here with an empty line between the
screenshots and the `<details>` tags.

</details>


# Changelog

:cl:
add: FTL vendors get signal flare packs for 5 points.
/:cl:

code/game/machinery/vending/vendor_types/squad_prep/squad_tl.dm

@@ -49,6 +49,7 @@ GLOBAL_LIST_INIT(cm_vending_gear_tl, list(
 
 		list("ENGINEERING SUPPLIES", 0, null, null, null),
 		list("Plastic Explosive", 10, /obj/item/explosive/plastic, null, VENDOR_ITEM_REGULAR),
+		list("Signal Flare Pack", 5, /obj/item/storage/box/m94/signal, null, VENDOR_ITEM_REGULAR),
 		list("Breaching Charge", 10, /obj/item/explosive/plastic/breaching_charge, null, VENDOR_ITEM_REGULAR),
 		list("ES-11 Mobile Fuel Canister", 5, /obj/item/tool/weldpack/minitank, null, VENDOR_ITEM_REGULAR),
 		list("ME3 Hand Welder", 5, /obj/item/tool/weldingtool/simple, null, VENDOR_ITEM_REGULAR),