FEATURE: Add Top Ignored Users report (#7153)

* FEATURE: Add `Top Ignored Users` report

## Why?

This is part of the [Ability to ignore a user feature](https://meta.discourse.org/t/ability-to-ignore-a-user/110254/8), and also part of [this PR](https://github.com/discourse/discourse/pull/7144).

We want to send a System Message daily when a specific count threshold for an ignored is reached. To make this system message informative, we want to link to a report for the Top Ignored Users too.

spec/models/report_spec.rb

@@ -1094,6 +1094,35 @@ describe Report do
     include_examples "no data"
   end
 
+  describe "report_top_ignored_users" do
+    let(:report) { Report.find("top_ignored_users") }
+    let(:tarek) { Fabricate(:user, username: "tarek") }
+    let(:john) { Fabricate(:user, username: "john") }
+    let(:matt) { Fabricate(:user, username: "matt") }
+
+    context "with data" do
+      before do
+        Fabricate(:ignored_user, user: tarek, ignored_user: john)
+        Fabricate(:ignored_user, user: tarek, ignored_user: matt)
+      end
+
+      it "works" do
+        expect(report.data.length).to eq(2)
+        expect_row_to_be_equal(report.data[0], john)
+        expect_row_to_be_equal(report.data[1], matt)
+      end
+
+      def expect_row_to_be_equal(row, user)
+        expect(row[:ignored_user_id]).to eq(user.id)
+        expect(row[:ignored_username]).to eq(user.username)
+        expect(row[:ignored_user_avatar_template]).to eq(User.avatar_template(user.username, user.uploaded_avatar_id))
+        expect(row[:ignores_count]).to eq(1)
+      end
+    end
+
+    include_examples "no data"
+  end
+
   describe "consolidated_page_views" do
     before do
       freeze_time(Time.now.at_midnight)