The 'Request OPFOR' verb now requires confirmation (#4978)

## About The Pull Request
Does as the title says. When you press the button, a pop-up now asks if
you are sure you want to press it.
## Why It's Good For The Game
I've watched a handful of staff members accidentally hit it in my time
here while trying to play web sounds, enough that I feel it warrants
this. Especially given that it pings every player with be antagonist
turned on.
## Proof Of Testing
<details>
<summary>Screenshots/Videos</summary>


https://github.com/user-attachments/assets/f59a26ec-5507-4cbb-b9f1-6c1300b1d10e

</details>

## Changelog
🆑
admin: The Request OPFOR verb now asks for confirmation before pinging
every antagonist enabled player for OPFORs.
/🆑

modular_skyrat/modules/opposing_force/code/admin_procs.dm

@@ -1,4 +1,8 @@
 ADMIN_VERB(request_more_opfor, R_FUN, "Request OPFOR", "Request players sign up for opfor if they have antag on.", ADMIN_CATEGORY_FUN)
+	var/confirm = tgui_alert(user, "Please confirm you want to ask all antagonist enabled players to submit an OPFOR?", "Confirm Request OPFOR", list("Yes", "No"))
+	if(confirm != "Yes")
+		return
+
 	var/asked = 0
 	for(var/mob/living/carbon/human/human in GLOB.alive_player_list)
 		if(human.client?.prefs?.read_preference(/datum/preference/toggle/be_antag))