Add a user-settings core nav item

As user-settings should show up in the core nav, add a user-settings nav
item to the declarative integration plugin.

Signed-off-by: Craig Tracey <craig@arctir.com>

.changeset/chilled-zebras-wash.md

@@ -0,0 +1,5 @@
+---
+'@backstage/plugin-user-settings': patch
+---
+
+add user-settings declarative integration core nav item

plugins/user-settings/api-report-alpha.md

@@ -4,6 +4,7 @@
 
 ```ts
 import { BackstagePlugin } from '@backstage/frontend-plugin-api';
+import { ExtensionDefinition } from '@backstage/frontend-plugin-api';
 import { RouteRef } from '@backstage/frontend-plugin-api';
 import { TranslationRef } from '@backstage/core-plugin-api/alpha';
 
@@ -16,6 +17,11 @@ const _default: BackstagePlugin<
 >;
 export default _default;
 
+// @alpha (undocumented)
+export const settingsNavItem: ExtensionDefinition<{
+  title: string;
+}>;
+
 // @alpha (undocumented)
 export const userSettingsTranslationRef: TranslationRef<
   'user-settings',

plugins/user-settings/src/alpha.tsx

@@ -16,6 +16,7 @@
 import {
   coreExtensionData,
   createExtensionInput,
+  createNavItemExtension,
   createPageExtension,
   createPlugin,
 } from '@backstage/frontend-plugin-api';
@@ -23,6 +24,7 @@ import {
   convertLegacyRouteRef,
   compatWrapper,
 } from '@backstage/core-compat-api';
+import SettingsIcon from '@material-ui/icons/Settings';
 import { settingsRouteRef } from './plugin';
 
 import React from 'react';
@@ -50,12 +52,19 @@ const userSettingsPage = createPageExtension({
     ),
 });
 
+/** @alpha */
+export const settingsNavItem = createNavItemExtension({
+  routeRef: convertLegacyRouteRef(settingsRouteRef),
+  title: 'Settings',
+  icon: SettingsIcon,
+});
+
 /**
  * @alpha
  */
 export default createPlugin({
   id: 'user-settings',
-  extensions: [userSettingsPage],
+  extensions: [userSettingsPage, settingsNavItem],
   routes: {
     root: convertLegacyRouteRef(settingsRouteRef),
   },