FEATURE: add category banner for why a user cannot post (#9576)

* FEATURE: add category banner for why a user cannot post

Adds a category banner for why a user is unable to post in a category.

Also adds an extra alert for the user when a user is unable to create a topic in a
category and they still try and click on the disabled-looking new topic
button.

test/javascripts/fixtures/discovery_fixtures.js

@@ -6120,5 +6120,107 @@ export default {
         }
       ]
     }
+  },
+  "/latest_can_create_topic.json": {
+    users: [
+      {
+        id: 1,
+        username: "tt1",
+        name: null,
+        avatar_template: "/letter_avatar_proxy/v4/letter/t/6de8d8/{size}.png"
+      }
+    ],
+    primary_groups: [],
+    topic_list: {
+      can_create_topic: true,
+      draft: null,
+      draft_key: "new_topic",
+      draft_sequence: 0,
+      per_page: 30,
+      topics: [
+        {
+          id: 30,
+          title: "I am also creating a new topic here new topic",
+          fancy_title: "I am also creating a new topic here new topic",
+          slug: "i-am-also-creating-a-new-topic-here-new-topic",
+          posts_count: 6,
+          reply_count: 0,
+          highest_post_number: 6,
+          image_url: null,
+          created_at: "2020-04-27T23:47:44.218Z",
+          last_posted_at: "2020-04-28T22:45:47.529Z",
+          bumped: true,
+          bumped_at: "2020-04-28T22:02:20.215Z",
+          archetype: "regular",
+          unseen: false,
+          last_read_post_number: 5,
+          unread: 0,
+          new_posts: 0,
+          pinned: false,
+          unpinned: null,
+          visible: true,
+          closed: false,
+          archived: false,
+          notification_level: 1,
+          bookmarked: false,
+          liked: false,
+          tags: ["test", "test-tag"],
+          views: 6,
+          like_count: 0,
+          has_summary: false,
+          last_poster_username: "tt1",
+          category_id: 5,
+          pinned_globally: false,
+          featured_link: null,
+          posters: [
+            {
+              extras: "latest single",
+              description: "Original Poster, Most Recent Poster",
+              user_id: 1,
+              primary_group_id: null
+            }
+          ]
+        },
+        {
+          id: 29,
+          title: "About the test category category",
+          fancy_title: "About the test category category",
+          slug: "about-the-test-category-category",
+          posts_count: 5,
+          reply_count: 0,
+          highest_post_number: 5,
+          image_url: null,
+          created_at: "2020-04-27T22:15:49.424Z",
+          last_posted_at: "2020-04-27T23:51:06.249Z",
+          bumped: true,
+          bumped_at: "2020-04-27T22:15:49.424Z",
+          archetype: "regular",
+          unseen: false,
+          pinned: false,
+          unpinned: null,
+          visible: true,
+          closed: false,
+          archived: false,
+          bookmarked: null,
+          liked: null,
+          tags: [],
+          views: 1,
+          like_count: 0,
+          has_summary: false,
+          last_poster_username: "tt1",
+          category_id: 5,
+          pinned_globally: false,
+          featured_link: null,
+          posters: [
+            {
+              extras: "latest single",
+              description: "Original Poster, Most Recent Poster",
+              user_id: 1,
+              primary_group_id: null
+            }
+          ]
+        }
+      ]
+    }
   }
 };