Remove invalid releases automatically (#466)

Automatically remove empty releases or releases which are released in the future, regardless of the product.

Also refactored a bit releasedata.py to use better names and clarify types.

releases/grafana.json

@@ -1,32 +1,5 @@
 {
   "releases": {
-    "9.5": {
-      "name": "9.5"
-    },
-    "9.4": {
-      "name": "9.4"
-    },
-    "9.3": {
-      "name": "9.3"
-    },
-    "9.2": {
-      "name": "9.2"
-    },
-    "9.1": {
-      "name": "9.1"
-    },
-    "9.0": {
-      "name": "9.0"
-    },
-    "8": {
-      "name": "8"
-    },
-    "7": {
-      "name": "7"
-    },
-    "6": {
-      "name": "6"
-    },
     "12.0": {
       "name": "12.0",
       "eol": "2026-01-31"
@@ -62,18 +35,6 @@
     "10.4": {
       "name": "10.4",
       "eol": "2025-06-30"
-    },
-    "10.3": {
-      "name": "10.3"
-    },
-    "10.2": {
-      "name": "10.2"
-    },
-    "10.1": {
-      "name": "10.1"
-    },
-    "10.0": {
-      "name": "10.0"
     }
   },
   "versions": {