Add filters by milestone, author, and assignee to task by type

The task by type internal API endpoints, used to produce the "Type of
work" chart, can now filter by author, by assignees, and by milestone.
This makes it consistent with the other charts on the same page.

Using the same convention as the other charts, the filters are specified
with the following URL parameters:

  - `milestone_title` - a string with the milestone title to filter for
  - `author_username` - the username of the author to filter for
  - `assignee_username` - it accepts a single username or multiple
    usernames (like
`assignee_username[]=username1&assignee_username[]=username2`) of
assignees to filter for.

Changelog: changed
EE: true

ee/app/controllers/groups/analytics/tasks_by_type_controller.rb

@@ -27,7 +27,10 @@ def tasks_by_type
       label_ids: Array(params[:label_ids]),
       project_ids: Array(params[:project_ids]),
       created_after: @created_after.to_time.utc.beginning_of_day,
-      created_before: @created_before.to_time.utc.end_of_day
+      created_before: @created_before.to_time.utc.end_of_day,
+      author_username: params[:author_username],
+      assignee_username: params[:assignee_username],
+      milestone_id: params[:milestone_id]
     })
   end

ee/lib/gitlab/analytics/type_of_work/tasks_by_type.rb

@@ -55,7 +55,10 @@ def format_result(result)
         end
         def finder_params
-          { include_subgroups: true, group_id: group.id }.merge(params.slice(:created_after, :created_before))
+          {
+            include_subgroups: true,
+            group_id: group.id
+          }.merge(params.slice(:created_after, :created_before, :author_username, :milestone_title, :assignee_username))
         end
         # rubocop: disable CodeReuse/ActiveRecord

ee/spec/lib/gitlab/analytics/type_of_work/tasks_by_type_spec.rb

@@ -13,6 +13,8 @@
   let_it_be(:label_for_subgroup) { create(:group_label, group: group) }
   let_it_be(:other_label) { create(:group_label, group: other_group) }
   let_it_be(:project) { create(:project, group: group) }
+  let_it_be(:assignee) { create(:user) }
+  let_it_be(:milestone) { create(:milestone, group: group) }
   let(:params) do
     {
@@ -32,6 +34,7 @@
   before do
     group.add_reporter(user)
+    group.add_developer(assignee)
   end
   shared_examples '#counts_by_labels' do
@@ -39,6 +42,8 @@
       create(factory_name, {
         :created_at => 3.days.ago,
         :labels => [label],
+        :assignees => [assignee],
+        :milestone => milestone,
         project_attribute_name => project
       })
     end
@@ -118,6 +123,30 @@ def label_count_for(label, result)
       it { expect(label_count_for(label, subject)).to eq(1) }
     end
+
+    context 'when filtering by `author_username`' do
+      before do
+        params[:params][:author_username] = with_label.author.username
+      end
+
+      it { expect(label_count_for(label, subject)).to eq(1) }
+    end
+
+    context 'when filtering by `assignee_username`' do
+      before do
+        params[:params][:assignee_username] = [assignee.username]
+      end
+
+      it { expect(label_count_for(label, subject)).to eq(1) }
+    end
+
+    context 'when filtering by `milestone_title`' do
+      before do
+        params[:params][:milestone_title] = milestone.title
+      end
+
+      it { expect(label_count_for(label, subject)).to eq(1) }
+    end
   end
   shared_examples '#top_labels' do