[silverstripe] Add method (#532)

Parse https://raw.githubusercontent.com/silverstripe/roadmap/refs/heads/main/data.json to get release information.

Relates to https://github.com/endoflife-date/endoflife.date/pull/8932.

releases/ubuntu.json

@@ -356,6 +356,10 @@
     "5.04": {
       "name": "5.04",
       "date": "2005-04-08"
+    },
+    "4.10": {
+      "name": "4.10",
+      "date": "2004-10-20"
     }
   }
 }