Switched Portal settings unsaved changes modal to new modal pattern

refs https://github.com/TryGhost/Team/issues/1734
refs https://github.com/TryGhost/Team/issues/559
refs https://github.com/TryGhost/Ghost/issues/14101

- switches to newer modal patterns ready for later Ember upgrades

ghost/admin/app/controllers/settings/membership.js

@@ -1,3 +1,4 @@
+import ConfirmUnsavedChangesModal from '../../components/modals/confirm-unsaved-changes';
 import Controller from '@ember/controller';
 import envConfig from 'ghost-admin/config/environment';
 import {action} from '@ember/object';
@@ -18,11 +19,11 @@ export default class MembersAccessController extends Controller {
     @service config;
     @service feature;
     @service membersUtils;
+    @service modals;
     @service settings;
     @service store;
     @service session;
 
-    @tracked showLeavePortalModal = false;
     @tracked showPortalSettings = false;
     @tracked showStripeConnect = false;
     @tracked showTierModal = false;
@@ -216,29 +217,23 @@ export default class MembersAccessController extends Controller {
     }
 
     @action
-    closePortalSettings() {
+    async closePortalSettings() {
         const changedAttributes = this.settings.changedAttributes();
+
         if (changedAttributes && Object.keys(changedAttributes).length > 0) {
-            this.showLeavePortalModal = true;
+            const shouldClose = await this.modals.open(ConfirmUnsavedChangesModal);
+
+            if (shouldClose) {
+                this.settings.rollbackAttributes();
+                this.showPortalSettings = false;
+                this.updatePortalPreview();
+            }
         } else {
             this.showPortalSettings = false;
             this.updatePortalPreview();
         }
     }
 
-    @action
-    async confirmClosePortalSettings() {
-        this.settings.rollbackAttributes();
-        this.showPortalSettings = false;
-        this.showLeavePortalModal = false;
-        this.updatePortalPreview();
-    }
-
-    @action
-    cancelClosePortalSettings() {
-        this.showLeavePortalModal = false;
-    }
-
     @action
     updatePortalPreview({forceRefresh} = {forceRefresh: false}) {
         // TODO: can these be worked out from settings in membersUtils?

ghost/admin/app/templates/settings/membership.hbs

@@ -161,7 +161,8 @@
     </section>
 
     {{#if this.showPortalSettings}}
-        <GhFullscreenModal @modal="portal-settings"
+        <GhFullscreenModal
+            @modal="portal-settings"
             @model={{hash
                 preloadTask=this.saveSettingsTask
                 openStripeConnect=this.openStripeConnect
@@ -171,15 +172,6 @@
             @modifier="full-overlay portal-settings" />
     {{/if}}
 
-    {{#if this.showLeavePortalModal}}
-        <GhFullscreenModal
-            @modal="leave-settings"
-            @confirm={{this.confirmClosePortalSettings}}
-            @close={{this.cancelClosePortalSettings}}
-            @modifier="action wide"
-        />
-    {{/if}}
-
     {{#if this.showStripeConnect}}
         <GhFullscreenModal
             @modal="stripe-connect"