Add "User Permissions" heading in permissions modal

Added "User Permissions" heading in the permissions modal, right above the "Add user" button.
Also: tweak spacing for "Public" heading and corresponding toggle

frontend/src/components/object/ObjectPermission.vue

@@ -87,13 +87,13 @@ onBeforeMount(() => {
   <div>
     <div class="flex flex-row gap-6 pb-3">
       <div>
-        <h3>Public</h3>
+        <h3 class="pb-1">Public</h3>
         <ul>
           <li>This option toggles the file to be publicly available and accessible to anyone</li>
           <li>To instead set explicit permissions, add users and use the options below</li>
         </ul>
       </div>
-      <div>
+      <div class="ml-4">
         <InputSwitch
           v-if="object"
           v-model="object.public"
@@ -106,6 +106,10 @@ onBeforeMount(() => {
       </div>
     </div>
 
+    <div class="mt-1 mb-2">
+      <h3>User Permissions</h3>
+    </div>
+
     <div v-if="!showSearchUsers">
       <Button
         class="mt-1 mb-4"