Added metric to derive new users count

Includes metric 'users_created' to report distinct number
of users created within the time duration.

changelogs/unreleased/user-creation-count.yml

+---
+title: Add metric to derive new users count
+merge_request: 27351
+author:
+type: added

doc/user/admin_area/settings/usage_statistics.md

@@ -402,6 +402,7 @@ but commented out to help encourage others to add to it in the future. -->
 |groups|usage_activity_by_stage|manage|
 |ldap_keys|usage_activity_by_stage|manage|
 |ldap_users: 0|usage_activity_by_stage|manage|
+|users_created|usage_activity_by_stage|manage|
 |clusters|usage_activity_by_stage|monitor|
 |clusters_applications_prometheus|usage_activity_by_stage|monitor|
 |operations_dashboard_default_dashboard|usage_activity_by_stage|monitor|

ee/app/models/ee/user.rb

@@ -16,6 +16,8 @@ module EE
     MAX_USERNAME_SUGGESTION_ATTEMPTS = 15
 
     prepended do
+      include UsageStatistics
+
       EMAIL_OPT_IN_SOURCE_ID_GITLAB_COM = 1
 
       # We aren't using the `auditor?` method for the `if` condition here

ee/lib/ee/gitlab/usage_data.rb

@@ -243,7 +243,8 @@ module EE
             events: distinct_count(::Event.where(time_period), :author_id),
             groups: distinct_count(::GroupMember.where(time_period), :user_id),
             ldap_keys: distinct_count(::LDAPKey.where(time_period), :user_id),
-            ldap_users: distinct_count(::GroupMember.of_ldap_type.where(time_period), :user_id)
+            ldap_users: distinct_count(::GroupMember.of_ldap_type.where(time_period), :user_id),
+            users_created: count(::User.where(time_period))
           }
         end
 

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

@@ -156,13 +156,15 @@ describe Gitlab::UsageData do
                 events: 2,
                 groups: 2,
                 ldap_keys: 2,
-                ldap_users: 2
+                ldap_users: 2,
+                users_created: 6
               )
               expect(described_class.uncached_data[:usage_activity_by_stage_monthly][:manage]).to eq(
                 events: 1,
                 groups: 1,
                 ldap_keys: 1,
-                ldap_users: 1
+                ldap_users: 1,
+                users_created: 4
               )
             end
           end