UX: Various improvements to welcome topic CTA (#21010)

- Update welcome topic copy
- Edit the welcome topic automatically when the title or description changes
- Remove “Create your Welcome Topic” banner/CTA
- Add "edit welcome topic" user tip

spec/requests/categories_controller_spec.rb

@@ -261,74 +261,6 @@ RSpec.describe CategoriesController do
       end
     end
 
-    describe "welcome topic" do
-      fab!(:category) { Fabricate(:category) }
-      fab!(:topic1) do
-        Fabricate(
-          :topic,
-          category: category,
-          created_at: 5.days.ago,
-          updated_at: Time.now,
-          bumped_at: Time.now,
-        )
-      end
-      fab!(:topic2) do
-        Fabricate(:topic, category: category, created_at: 2.days.ago, bumped_at: 2.days.ago)
-      end
-      fab!(:topic3) do
-        Fabricate(:topic, category: category, created_at: 1.day.ago, bumped_at: 1.day.ago)
-      end
-      fab!(:welcome_topic) { Fabricate(:topic) }
-      fab!(:post) { Fabricate(:post, topic: welcome_topic) }
-
-      before do
-        SiteSetting.desktop_category_page_style = "categories_and_latest_topics"
-        SiteSetting.welcome_topic_id = welcome_topic.id
-        SiteSetting.editing_grace_period = 1.minute.to_i
-        SiteSetting.bootstrap_mode_enabled = true
-      end
-
-      it "is hidden for non-admins" do
-        get "/categories_and_latest.json"
-        expect(response.status).to eq(200)
-        expect(response.parsed_body["topic_list"]["topics"].map { |t| t["id"] }).not_to include(
-          welcome_topic.id,
-        )
-      end
-
-      it "is shown to non-admins when there is an edit" do
-        post.revise(post.user, { raw: "#{post.raw}2" }, revised_at: post.updated_at + 2.minutes)
-        post.reload
-        expect(post.version).to eq(2)
-
-        get "/categories_and_latest.json"
-        expect(response.status).to eq(200)
-        expect(response.parsed_body["topic_list"]["topics"].map { |t| t["id"] }).to include(
-          welcome_topic.id,
-        )
-      end
-
-      it "is hidden to admins" do
-        sign_in(admin)
-
-        get "/categories_and_latest.json"
-        expect(response.status).to eq(200)
-        expect(response.parsed_body["topic_list"]["topics"].map { |t| t["id"] }).not_to include(
-          welcome_topic.id,
-        )
-      end
-
-      it "is shown to users when bootstrap mode is disabled" do
-        SiteSetting.bootstrap_mode_enabled = false
-
-        get "/categories_and_latest.json"
-        expect(response.status).to eq(200)
-        expect(response.parsed_body["topic_list"]["topics"].map { |t| t["id"] }).to include(
-          welcome_topic.id,
-        )
-      end
-    end
-
     it "includes subcategories and topics by default when view is subcategories_with_featured_topics" do
       SiteSetting.max_category_nesting = 3
       subcategory = Fabricate(:category, user: admin, parent_category: category)