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/insurgency_sandstorm/egg-insurgency--sandstorm.json

@@ -8,7 +8,9 @@
     "name": "Insurgency: Sandstorm",
     "author": "brycea@terrahost.cloud",
     "description": "Insurgency: Sandstorm is a team-based, tactical FPS based on lethal close quarters combat and objective-oriented multiplayer gameplay. Experience the intensity of modern combat where skill is rewarded, and teamwork wins the fight.",
-    "features": null,
+    "features": [
+        "steam_disk_space"
+    ],
     "images": [
         "ghcr.io\/parkervcp\/games:source"
     ],
@@ -92,4 +94,4 @@
             "rules": "required|string|max:20"
         }
     ]
-}
+}