Add smtp_server to usage ping data

Send the value of the smtp_server along with usage ping

changelogs/unreleased/238111-count-of-the-number-of-self-hosted-smtp-configurations-by-package.yml

+---
+title: Add smtp_server to usage ping data
+merge_request: 39844
+author:
+type: changed

lib/gitlab/usage_data.rb

@@ -269,6 +269,9 @@ module Gitlab
           database: {
             adapter: alt_usage_data { Gitlab::Database.adapter_name },
             version: alt_usage_data { Gitlab::Database.version }
+          },
+          mail: {
+            smtp_server: alt_usage_data { ActionMailer::Base.smtp_settings[:address] }
           }
         }
       end

rubocop/rubocop-usage-data.yml

@@ -4,6 +4,7 @@ UsageData/LargeTable:
     - 'lib/gitlab/usage_data.rb'
     - 'ee/lib/ee/gitlab/usage_data.rb'
   NonRelatedClasses:
+    - :ActionMailer::Base
     - :Date
     - :Feature
     - :Gitlab

spec/lib/gitlab/usage_data_spec.rb

@@ -673,6 +673,7 @@ RSpec.describe Gitlab::UsageData, :aggregate_failures do
         expect(subject[:git][:version]).to eq(Gitlab::Git.version)
         expect(subject[:database][:adapter]).to eq(Gitlab::Database.adapter_name)
         expect(subject[:database][:version]).to eq(Gitlab::Database.version)
+        expect(subject[:mail][:smtp_server]).to eq(ActionMailer::Base.smtp_settings[:address])
         expect(subject[:gitaly][:version]).to be_present
         expect(subject[:gitaly][:servers]).to be >= 1
         expect(subject[:gitaly][:clusters]).to be >= 0