[Geo node status improvements] Address review comments

lib/tasks/geo.rake

@@ -271,8 +271,8 @@ namespace :geo do
     if current_node_status.updated_at
       puts "#{time_ago_in_words(current_node_status.updated_at)} ago"
     else
-      # Only primary node can create a status record in the database so if it's not exists
-      # we get not persistant AR record here.
+      # Only primary node can create a status record in the database so if it does not exist
+      # we get unsaved record where updated_at is nil
       puts "Never"
     end
   end

spec/ee/fixtures/api/schemas/public_api/v4/geo_node_status.json

@@ -33,7 +33,8 @@
     "namespaces",
     "version",
     "revision",
-    "_links"
+    "_links",
+    "updated_at"
   ],
   "properties" : {
     "geo_node_id": { "type": "integer" },
@@ -84,7 +85,8 @@
         "node": { "type": "string" }
       },
       "additionalProperties": false
-    }
+    },
+    "updated_at": { "type": ["string", "null"] }
   },
   "additionalProperties": false
 }