Investigate logs include ckey of source (if applicable) (#71833)

## About The Pull Request
All investigate logs start with [src], which can be any atom. So
sometimes names and items get printed twice. Adds ckeys to the
investigate_logs of living mobs.


![image](https://user-images.githubusercontent.com/66640614/206372340-3c50bc9d-b662-4a4d-b1ec-91c0b4db8a39.png)


## Why It's Good For The Game
Better logging, includes the ckey for living mobs in investigate logs,
and fixes some investigate_death logs that weren't properly attributed
to mobs.

## Changelog

🆑 Tattle
admin: investigate logs include ckey of source (if applicable)
/🆑

Co-authored-by: tattle <article.disaster@gmail.com>

code/modules/admin/admin_investigate.dm

@@ -2,7 +2,13 @@
 	if(!message || !subject)
 		return
 	var/F = file("[GLOB.log_directory]/[subject].html")
-	WRITE_FILE(F, "[time_stamp()] [REF(src)] ([x],[y],[z]) || [src] [message]<br>")
+	var/source = "[src]"
+
+	if(isliving(src))
+		var/mob/living/source_mob = src
+		source += " ([source_mob.ckey ? source_mob.ckey : "*no key*"])"
+
+	WRITE_FILE(F, "[time_stamp()] [REF(src)] ([x],[y],[z]) || [source] [message]<br>")
 
 /client/proc/investigate_show()
 	set name = "Investigate"