Delay tool form rendering until config is loaded

The config typically is already loaded once you hit the tool form,
so this shouldn't cause a delay, and we already do the same effectively
for the current user and current history id.

Fixes #18139
```
TypeError: e.config is null
  at $b (webpack://@galaxyproject/galaxy-client/./src/components/Tool/ToolForm.vue?5639:1:1709)
  at Vue.prototype._render (webpack://@galaxyproject/galaxy-client/./node_modules/vue/dist/vue.esm.js:2540:28)
  at updateComponent (webpack://@galaxyproject/galaxy-client/./node_modules/vue/dist/vue.esm.js:2980:27)
  at Watcher.prototype.get (webpack://@galaxyproject/galaxy-client/./node_modules/vue/dist/vue.esm.js:4164:33)
  at Watcher.prototype.run (webpack://@galaxyproject/galaxy-client/./node_modules/vue/dist/vue.esm.js:4240:30)
...
(3 additional frame(s) were not displayed)
```

client/src/components/Tool/ToolForm.vue

@@ -1,5 +1,5 @@
 <template>
-    <div v-if="currentUser && currentHistoryId">
+    <div v-if="currentUser && currentHistoryId && isConfigLoaded">
         <b-alert :show="messageShow" :variant="messageVariant">
             {{ messageText }}
         </b-alert>