feat: add steam_disk_space egg feature to SteamCMD eggs

A new egg feature modal was introduced in Panel v1.7.0 triggering when server has run out of disk space to provide more user-friendly instructions to both admins and normal users. This is unique to SteamCMD specific errors.

game_eggs/steamcmd_servers/citadel/egg-citadel-forged-with-fire.json

@@ -8,7 +8,9 @@
     "name": "Citadel: Forged with Fire",
     "author": "info@goover.de",
     "description": "Citadel: Forged With Fire is a massive online sandbox RPG set in the mystical world of Ignus. Featuring magic, spellcasting, building, exploring and crafting as you fight to make a name for yourself and achieve notoriety across the land.",
-    "features": null,
+    "features": [
+        "steam_disk_space"
+    ],
     "images": [
         "ghcr.io\/parkervcp\/games:source"
     ],
@@ -65,4 +67,4 @@
             "rules": "required|string|max:20"
         }
     ]
-}
+}