Plantable UPP Flag (#6927)

# About the pull request

Adds a plantable UPP flag to the game, akin to the plantable USCM
version. Currently does not spawn anywhere in-game.

# Explain why it's good for the game

Soul. 

Essentially another thing for OpFor to rally around, inspire motivation
and atmosphere.

Video below showcasing the audio. Special thanks to @VileBeggar for the
audio.


# Testing Photographs and Procedure
<details>
<summary>Screenshots & Videos</summary>

![Screenshot 2024-08-11 21 01
32](https://github.com/user-attachments/assets/843d448e-6cfd-46b6-8d71-acb1e43f2a2d)



https://github.com/user-attachments/assets/bebc7672-23e0-42e2-9b4a-e0490ec3e68f



</details>


# Changelog
:cl:
add: A plantable UPP flag has been added to the game, an equilivant of
the United Americas flag. Currently admin spawn only.
/:cl:

---------

Co-authored-by: Steelpoint <[email protected]>
Co-authored-by: Blundir <[email protected]>

code/game/objects/items/stacks/flags.dm

@@ -281,3 +281,23 @@
 	desc = "The flag of the United Americas. Semper fi."
 	icon_state = "flag_ua_planted"
 	flag_type = /obj/item/flag/plantable/ua
+
+// UNION OF PROGRESSIVE PEOPLES FLAG //
+//////////////////////////
+
+/obj/item/flag/plantable/upp
+	name = "\improper Union of Progressive Peoples flag"
+	desc = "The flag of the Union of Progressive Peoples. This one looks ready to be planted into the ground."
+	icon = 'icons/obj/structures/plantable_flag.dmi'
+	icon_state = "flag_upp"
+	flag_type = /obj/structure/flag/plantable/upp
+	faction = FACTION_UPP
+	play_warcry = TRUE
+	warcry_sound = 'sound/effects/flag_upp_warcry.ogg'
+	warcry_extra_sound = 'sound/effects/flag_upp_warcry_extra.ogg'
+
+/obj/structure/flag/plantable/upp
+	name = "\improper Union of Progressive Peoples flag"
+	desc = "The flag of the Union of Progressive Peoples. Unity through Strength, Freedom through Unity."
+	icon_state = "flag_upp_planted"
+	flag_type = /obj/item/flag/plantable/upp