DEV: Add new experimental admin UI route and sidebar (#23952)

This commit adds a new admin UI under the route `/admin-revamp`, which is
only accessible if the user is in a group defined by the new `enable_experimental_admin_ui_groups` site setting. It
also adds a special `admin` sidebar panel that is shown instead of the `main`
forum one when the admin is in this area.

![image](https://github.com/discourse/discourse/assets/920448/fa0f25e1-e178-4d94-aa5f-472fd3efd787)

We also add an "Admin Revamp" sidebar link to the community section, which
will only appear if the user is in the setting group:

![image](https://github.com/discourse/discourse/assets/920448/ec05ca8b-5a54-442b-ba89-6af35695c104)

Within this there are subroutes defined like `/admin-revamp/config/:area`,
these areas could contain any UI imaginable, this is just laying down an
initial idea of the structure and how the sidebar will work. Sidebar links are
currently hardcoded.

Some other changes:

* Changed the `main` and `chat` panels sidebar panel keys to use exported const values for reuse
* Allowed custom sidebar sections to hide their headers with the `hideSectionHeader` option
* Add a `groupSettingArray` setting on `this.siteSettings` in JS, which accepts a group site setting name
  and splits it by `|` then converts the items in the array to integers, similar to the `_map` magic for ruby
  group site settings
* Adds a `hidden` option for sidebar panels which prevents them from showing in separated mode and prevents
  the switch button from being shown

---------

Co-authored-by: Krzysztof Kotlarek <kotlarek.krzysztof@gmail.com>

app/assets/javascripts/admin/addon/controllers/admin-revamp.js

@@ -0,0 +1,31 @@
+import Controller from "@ember/controller";
+import { inject as service } from "@ember/service";
+import { dasherize } from "@ember/string";
+import discourseComputed from "discourse-common/utils/decorators";
+
+export default class AdminRevampController extends Controller {
+  @service router;
+
+  @discourseComputed("router._router.currentPath")
+  adminContentsClassName(currentPath) {
+    let cssClasses = currentPath
+      .split(".")
+      .filter((segment) => {
+        return (
+          segment !== "index" &&
+          segment !== "loading" &&
+          segment !== "show" &&
+          segment !== "admin"
+        );
+      })
+      .map(dasherize)
+      .join(" ");
+
+    // this is done to avoid breaking css customizations
+    if (cssClasses.includes("dashboard")) {
+      cssClasses = `${cssClasses} dashboard-next`;
+    }
+
+    return cssClasses;
+  }
+}

app/assets/javascripts/admin/addon/routes/admin-revamp-config-area.js

@@ -0,0 +1,10 @@
+import Route from "@ember/routing/route";
+import { inject as service } from "@ember/service";
+
+export default class AdminRevampConfigAreaRoute extends Route {
+  @service router;
+
+  async model(params) {
+    return { area: params.area };
+  }
+}

app/assets/javascripts/admin/addon/routes/admin-revamp-config.js

@@ -0,0 +1,6 @@
+import Route from "@ember/routing/route";
+import { inject as service } from "@ember/service";
+
+export default class AdminRevampConfigRoute extends Route {
+  @service router;
+}

app/assets/javascripts/admin/addon/routes/admin-revamp-lobby.js

@@ -0,0 +1,6 @@
+import Route from "@ember/routing/route";
+import { inject as service } from "@ember/service";
+
+export default class AdminRevampLobbyRoute extends Route {
+  @service router;
+}

app/assets/javascripts/admin/addon/routes/admin-revamp.js

@@ -0,0 +1,40 @@
+import { inject as service } from "@ember/service";
+import DiscourseURL from "discourse/lib/url";
+import DiscourseRoute from "discourse/routes/discourse";
+import { ADMIN_PANEL, MAIN_PANEL } from "discourse/services/sidebar-state";
+import I18n from "discourse-i18n";
+
+export default class AdminRoute extends DiscourseRoute {
+  @service siteSettings;
+  @service currentUser;
+  @service sidebarState;
+
+  titleToken() {
+    return I18n.t("admin_title");
+  }
+
+  activate() {
+    if (
+      !this.currentUser.isInAnyGroups(
+        this.siteSettings.groupSettingArray(
+          "enable_experimental_admin_ui_groups"
+        )
+      )
+    ) {
+      return DiscourseURL.redirectTo("/admin");
+    }
+
+    this.sidebarState.setPanel(ADMIN_PANEL);
+    this.sidebarState.setSeparatedMode();
+    this.sidebarState.hideSwitchPanelButtons();
+
+    this.controllerFor("application").setProperties({
+      showTop: false,
+    });
+  }
+
+  deactivate() {
+    this.controllerFor("application").set("showTop", true);
+    this.sidebarState.setPanel(MAIN_PANEL);
+  }
+}

app/assets/javascripts/admin/addon/routes/admin-route-map.js

@@ -211,4 +211,14 @@ export default function () {
       }
     );
   });
+
+  // EXPERIMENTAL: These admin routes are hidden behind an `enable_experimental_admin_ui_groups`
+  // site setting and are subject to constant change.
+  this.route("admin-revamp", { resetNamespace: true }, function () {
+    this.route("lobby", { path: "/" }, function () {});
+
+    this.route("config", { path: "config" }, function () {
+      this.route("area", { path: "/:area" });
+    });
+  });
 }

app/assets/javascripts/admin/addon/templates/admin-revamp-config-area.hbs

@@ -0,0 +1,3 @@
+<div class="admin-revamp__config-area">
+  Config Area ({{@model.area}})
+</div>

app/assets/javascripts/admin/addon/templates/admin-revamp-config.hbs

@@ -0,0 +1,5 @@
+<div class="admin-revamp__config">
+  Config
+
+  {{outlet}}
+</div>

app/assets/javascripts/admin/addon/templates/admin-revamp-lobby.hbs

@@ -0,0 +1 @@
+Admin Revamp Lobby

app/assets/javascripts/admin/addon/templates/admin-revamp.hbs

@@ -0,0 +1,12 @@
+{{hide-application-footer}}
+<AdminWrapper @class="container">
+  <div class="row">
+    <div class="full-width">
+      <div class="boxed white admin-content">
+        <div class="admin-contents {{this.adminContentsClassName}}">
+          {{outlet}}
+        </div>
+      </div>
+    </div>
+  </div>
+</AdminWrapper>