Enable MailChimp email auto-categorisation

So that we don't have to file them away manually each time

data/admin.yml

@@ -22,6 +22,13 @@ subscribe_form:
     name: 'EMAIL'
   honeypot:
     name: 'b_63d185e7c795f2758d0d07c8b_81720ca987'
+  hidden_toggles:
+    - value: '1'
+      name: 'group[5838][1]'
+      id: 'mce-group[5838]-5838-0'
+    - value: '2'
+      name: 'group[5838][2]'
+      id: 'mce-group[5838]-5838-1'
 
 nav_home:
   - title: Home

src/components/subscribeForm.vue

@@ -20,6 +20,15 @@
           :name="Admin.subscribe_form && Admin.subscribe_form.honeypot.name || 'nothing'"
         />
       </div>
+      <div v-if="Admin.subscribe_form && Admin.subscribe_form.hidden_toggles">
+        <input
+          v-for="field in Admin.subscribe_form.hidden_toggles"
+          type="hidden"
+          :name="field.name"
+          :value="field.value || 'true'"
+          :id="field.id || null"
+        />
+      </div>
     </div>
 
     <button id="" class="" type="submit">