FEATURE: allow sidebar section api to create external links (#22609)

* FEATURE: allow sidebar section api to create external links

Right now, sidebar API allows creating sections with internal links. It should be extended to allow creating links to external URLs as well.

* FIX: after rebase

app/assets/javascripts/discourse/app/components/sidebar/api-sections.hbs

@@ -17,6 +17,7 @@
         @route={{link.route}}
         @model={{link.model}}
         @models={{link.models}}
+        @href={{link.href}}
         @title={{link.title}}
         @contentCSSClass={{link.contentCSSClass}}
         @prefixColor={{link.prefixColor}}

app/assets/javascripts/discourse/app/lib/sidebar/base-custom-sidebar-section-link.js

@@ -19,9 +19,12 @@ export default class BaseCustomSidebarSectionLink {
   /**
    * @returns {string} The Ember route which the section link should link to.
    */
-  get route() {
-    this._notImplemented();
-  }
+  get route() {}
+
+  /**
+   * @returns {string} URL to external website which the section link should link to.
+   */
+  get href() {}
 
   /**
    * @returns {Object} `model` argument for the <LinkTo> component. See https://api.emberjs.com/ember/release/classes/Ember.Templates.components/methods/LinkTo?anchor=LinkTo.

app/assets/javascripts/discourse/tests/acceptance/sidebar-plugin-api-test.js

@@ -206,6 +206,28 @@ acceptance("Sidebar - Plugin API", function (needs) {
                     return "hover button title attribute";
                   }
                 })(),
+
+                new (class extends BaseCustomSidebarSectionLink {
+                  get name() {
+                    return "homepage";
+                  }
+
+                  get classNames() {
+                    return "my-class-name";
+                  }
+
+                  get href() {
+                    return "https://www.discourse.org";
+                  }
+
+                  get title() {
+                    return "Homepage";
+                  }
+
+                  get text() {
+                    return "Homepage";
+                  }
+                })(),
               ];
             }
           };
@@ -349,6 +371,18 @@ acceptance("Sidebar - Plugin API", function (needs) {
       "uses correct prefix image url"
     );
 
+    assert.strictEqual(
+      links[3].title,
+      "Homepage",
+      "displays external link with correct title attribute"
+    );
+
+    assert.strictEqual(
+      links[3].href,
+      "https://www.discourse.org/",
+      "displays external link with correct href attribute"
+    );
+
     assert.strictEqual(
       query(".sidebar-section-link-hover button").title,
       "hover button title attribute",