feat: create a version.json file for all version of the docs sites to load version info from (#539)

Author: josephperrott

material.angular.io/firebase.json

@@ -8,6 +8,13 @@
         "destination": "/index.html"
       }
     ],
+    "headers": [{
+      "source" : "/assets/versions.json",
+      "headers" : [{
+        "key" : "Access-Control-Allow-Origin",
+        "value" : "*"
+      }]
+    }],
     "ignore": [
       "firebase.json",
       "**/node_modules/**",