Move merge_requests_users metric to stage section

The `merge_requests_users` metric is specific to create stage so
it's more appropriate to move it to the appropriate section.

changelogs/unreleased/pb-move-merge-requests-users-metric.yml

+---
+title: Move merge_requests_users metric to stage section
+merge_request: 35593
+author:
+type: changed

doc/development/telemetry/usage_ping.md

@@ -665,6 +665,7 @@ appear to be associated to any of the services running, since they all appear to
 | `ci_triggers`                                             | `usage_activity_by_stage`            | `verify`      |                  |         | Triggers enabled                                                           |
 | `clusters_applications_runner`                            | `usage_activity_by_stage`            | `verify`      |                  |         | Unique clusters with Runner enabled                                        |
 | `projects_reporting_ci_cd_back_to_github: 0`              | `usage_activity_by_stage`            | `verify`      |                  |         | Unique projects with a GitHub pipeline enabled                             |
+| `merge_requests_users`                                    | `usage_activity_by_stage_monthly`    | `create`      |                  |         | Unique count of users who used a merge request                             |
 | `nodes`                                                   | `topology`                           | `enablement`  |                  |         | The list of server nodes on which GitLab components are running            |
 | `duration_s`                                              | `topology`                           | `enablement`  |                  |         | Time it took to collect topology data                                      |
 | `node_memory_total_bytes`                                 | `topology > nodes`                   | `enablement`  |                  |         | The total available memory of this node                                    |

ee/spec/lib/ee/gitlab/usage_data_spec.rb

@@ -360,6 +360,7 @@ RSpec.describe Gitlab::UsageData do
             keys: 1,
             merge_requests: 6,
             projects_enforcing_code_owner_approval: 0,
+            merge_requests_users: 0,
             merge_requests_with_optional_codeowners: 2,
             merge_requests_with_required_codeowners: 4,
             projects_imported_from_github: 1,

lib/gitlab/usage_data.rb

@@ -159,8 +159,7 @@ module Gitlab
             usage_counters,
             user_preferences_usage,
             ingress_modsecurity_usage,
-            container_expiration_policies_usage,
-            merge_requests_usage(last_28_days_time_period)
+            container_expiration_policies_usage
           ).tap do |data|
             data[:snippets] = data[:personal_snippets] + data[:project_snippets]
           end
@@ -405,23 +404,19 @@ module Gitlab
       end
 
       # rubocop: disable CodeReuse/ActiveRecord
-      def merge_requests_usage(time_period)
+      def merge_requests_users(time_period)
         query =
           Event
             .where(target_type: Event::TARGET_TYPES[:merge_request].to_s)
             .where(time_period)
 
-        merge_request_users = distinct_count(
+        distinct_count(
           query,
           :author_id,
           batch_size: 5_000, # Based on query performance, this is the optimal batch size.
           start: User.minimum(:id),
           finish: User.maximum(:id)
         )
-
-        {
-          merge_requests_users: merge_request_users
-        }
       end
       # rubocop: enable CodeReuse/ActiveRecord
 
@@ -477,9 +472,10 @@ module Gitlab
       end
       # rubocop: enable CodeReuse/ActiveRecord
 
-      # Omitted because no user, creator or author associated: `lfs_objects`, `pool_repositories`, `web_hooks`
       def usage_activity_by_stage_create(time_period)
-        {}
+        {}.tap do |h|
+          h[:merge_requests_users] = merge_requests_users(time_period) if time_period.present?
+        end
       end
 
       # Omitted because no user, creator or author associated: `campaigns_imported_from_github`, `ldap_group_links`

spec/lib/gitlab/usage_data_spec.rb

@@ -77,6 +77,22 @@ RSpec.describe Gitlab::UsageData, :aggregate_failures do
       end
     end
 
+    context 'for create' do
+      it 'include usage_activity_by_stage data' do
+        expect(described_class.uncached_data[:usage_activity_by_stage][:create])
+          .not_to include(
+            :merge_requests_users
+          )
+      end
+
+      it 'includes monthly usage_activity_by_stage data' do
+        expect(described_class.uncached_data[:usage_activity_by_stage_monthly][:create])
+          .to include(
+            :merge_requests_users
+          )
+      end
+    end
+
     it 'ensures recorded_at is set before any other usage data calculation' do
       %i(alt_usage_data redis_usage_data distinct_count count).each do |method|
         expect(described_class).not_to receive(method)
@@ -662,7 +678,7 @@ RSpec.describe Gitlab::UsageData, :aggregate_failures do
     end
   end
 
-  describe '.merge_requests_usage' do
+  describe '.merge_requests_users' do
     let(:time_period) { { created_at: 2.days.ago..Time.current } }
     let(:merge_request) { create(:merge_request) }
     let(:other_user) { create(:user) }
@@ -679,9 +695,7 @@ RSpec.describe Gitlab::UsageData, :aggregate_failures do
     end
 
     it 'returns the distinct count of users using merge requests (via events table) within the specified time period' do
-      expect(described_class.merge_requests_usage(time_period)).to eq(
-        merge_requests_users: 2
-      )
+      expect(described_class.merge_requests_users(time_period)).to eq(2)
     end
   end
 

spec/support/helpers/usage_data_helpers.rb

@@ -78,7 +78,6 @@ module UsageDataHelpers
       labels
       lfs_objects
       merge_requests
-      merge_requests_users
       milestone_lists
       milestones
       notes