add greeting id for playwright tests

src/dfx/assets/project_templates/react/src/__frontend_name__/src/App.jsx

@@ -15,7 +15,7 @@ function App() {
   return (
     <main className="container">
       <div className="card">
-        <h1>{greeting}</h1>
+        <h1 id="greeting">{greeting}</h1>
         <form action="#" onSubmit={handleSubmit}>
           <label htmlFor="name">Enter your name:</label>
           <input type="text" id="name" required />

src/dfx/assets/project_templates/svelte/src/__frontend_name__/src/routes/+page.svelte

@@ -13,7 +13,7 @@
 
 <main class="container">
   <div class="card">
-    <h1>{greeting}</h1>
+    <h1 id="greeting">{greeting}</h1>
     <form action="#" on:submit|preventDefault={onSubmit}>
       <label for="name">Enter your name:</label>
       <input type="text" id="name" required />

src/dfx/assets/project_templates/vanilla_js/src/__frontend_name__/src/App.js

@@ -20,7 +20,7 @@ class App {
     let body = html`
         <main class="container">
             <div class="card">
-                <h1>${this.greeting}</h1>
+                <h1 id="greeting">${this.greeting}</h1>
                 <form action="#">
                     <label for="name">Enter your name:</label>
                     <input type="text" id="name" required />

src/dfx/assets/project_templates/vue/src/__frontend_name__/src/App.vue

@@ -15,7 +15,7 @@ async function handleSubmit(e) {
 <template>
   <main class="container">
     <div class="card">
-      <h1>{{ greeting }}</h1>
+      <h1 id="greeting">{{ greeting }}</h1>
 
       <form action="#" @submit="handleSubmit">
         <label for="name">Enter your name:</label>