feat(settings): add variable hints for webhook body template

src/views/Settings.vue

@@ -108,6 +108,13 @@
                     <div class="form-group">
                         <label>Body Template</label>
                         <textarea v-model="webhookSettings.body" rows="4" placeholder='{"subject":"Alert","text":"Message"}'></textarea>
+                        <p v-pre class="field-hint">
+                            Available variables in Body: {{ exceptionMsg }}, {{ serviceName }}, {{ exceptionType }}
+                            <br>
+                            - {{ exceptionMsg }}: The exception message, e.g. "Process superfrpc_test_test is dead"<br>
+                            - {{ serviceName }}: The service name, e.g. "superfrpc_test_test"<br>
+                            - {{ exceptionType }}: The type of exception, e.g. "Process Dead"
+                        </p>
                     </div>
                 </div>
                 <div class="form-actions">
@@ -385,4 +392,11 @@ textarea:focus {
 .webhook-modal {
     width: 600px;
 }
+
+.field-hint {
+    margin: 6px 0 0;
+    color: var(--text-secondary);
+    font-size: 13px;
+    line-height: 1.4;
+}
 </style>