add submit to enter functionality for endpoint preview

Before, if you modified the URL and pressed enter in the box, the whole page would reload. Now it simply sends the request

src/components/Preview.vue

@@ -264,10 +264,16 @@ const onError = (error) => {
 
 <template>
   <main>
-    <el-form ref="requestFormRef" :model="requestForm">
+    <el-form ref="requestFormRef" :model="requestForm" @submit.prevent>
       <el-form-item prop="url">
         <div class="flex-request-preview-panel">
-          <input type="text" v-model="url" :set="(requestForm.url = url)" id="search-input" />
+          <input 
+            type="text" 
+            v-model="url" 
+            :set="(requestForm.url = url)" 
+            id="search-input" 
+            @keyup.enter="submit(requestFormRef, submitRequest)"
+          />
           <el-button
             :type="type"
             id="search-button"