Improved default post access for bulk modal

refs https://github.com/TryGhost/Team/issues/2677

- Use post access level by default when doing single selection
- Use default access level from settings when selecting multiple posts

ghost/admin/app/components/posts-list/modals/edit-posts-access.hbs

@@ -1,4 +1,4 @@
-<div class="modal-content" data-test-modal="edit-posts-access">
+<div class="modal-content" data-test-modal="edit-posts-access" {{did-insert this.setup}}>
     <header class="modal-header">
         <h1>Modify access for {{if @data.selectionList.isSingle 'this post' (concat @data.selectionList.count ' posts')}}</h1>
     </header>

ghost/admin/app/components/posts-list/modals/edit-posts-access.js

@@ -6,12 +6,30 @@ import {tracked} from '@glimmer/tracking';
 
 export default class EditPostsAccessModal extends Component {
     @service store;
+    @service settings;
 
     // We createa new post model to use the same validations as the post model
-    @tracked post = this.store.createRecord('post', {
-        visibility: 'public',
-        tiers: []
-    });
+    @tracked post = this.store.createRecord('post', {});
+
+    get selectionList() {
+        return this.args.data.selectionList;
+    }
+
+    @action
+    setup() {
+        if (this.selectionList.first && this.selectionList.isSingle) {
+            this.post.set('visibility', this.selectionList.first.visibility);
+            this.post.set('tiers', this.selectionList.first.tiers);
+        } else {
+            // Use default
+            this.post.set('visibility', this.settings.defaultContentVisibility);
+            this.post.set('tiers', this.settings.defaultContentVisibilityTiers.map((tier) => {
+                return {
+                    id: tier
+                };
+            }));
+        }
+    }
 
     async validate() {
         // Mark as not new