Add unattended database migration option

- Adds an unattended database migration option supporting the use of
  automation and orchestration wrappers that need an indicator for when
  a step has made changes to the remote system

Related https://gitlab.com/gitlab-org/gitlab-orchestrator/-/issues/198Signed-off-by: Robert Marshall <rmarshall@gitlab.com>

changelogs/unreleased/198-add-automation-friendly-migration-rake-tasks.yml

+---
+title: Add unattended database migration option
+merge_request: 44392
+author:
+type: added

lib/tasks/gitlab/db.rake

@@ -65,6 +65,19 @@ namespace :gitlab do
       end
     end
 
+    desc 'GitLab | DB | Run database migrations and print `unattended_migrations_completed` if action taken'
+    task unattended: :environment do
+      no_database = !ActiveRecord::Base.connection.schema_migration.table_exists?
+      needs_migrations = ActiveRecord::Base.connection.migration_context.needs_migration?
+
+      if no_database || needs_migrations
+        Rake::Task['gitlab:db:configure'].invoke
+        puts "unattended_migrations_completed"
+      else
+        puts "unattended_migrations_static"
+      end
+    end
+
     desc 'GitLab | DB | Checks if migrations require downtime or not'
     task :downtime_check, [:ref] => :environment do |_, args|
       abort 'You must specify a Git reference to compare with' unless args[:ref]

spec/tasks/gitlab/db_rake_spec.rb

@@ -98,6 +98,29 @@ RSpec.describe 'gitlab:db namespace rake task' do
     end
   end
 
+  describe 'unattended' do
+    using RSpec::Parameterized::TableSyntax
+
+    where(:schema_migration_table_exists, :needs_migrations, :rake_output) do
+      false | false | "unattended_migrations_completed"
+      false | true | "unattended_migrations_completed"
+      true | false | "unattended_migrations_static"
+      true | true | "unattended_migrations_completed"
+    end
+
+    before do
+      allow(Rake::Task['gitlab:db:configure']).to receive(:invoke).and_return(true)
+    end
+
+    with_them do
+      it 'outputs changed message for automation after operations happen' do
+        allow(ActiveRecord::Base.connection.schema_migration).to receive(:table_exists?).and_return(schema_migration_table_exists)
+        allow_any_instance_of(ActiveRecord::MigrationContext).to receive(:needs_migration?).and_return(needs_migrations)
+        expect { run_rake_task('gitlab:db:unattended') }. to output(/^#{rake_output}$/).to_stdout
+      end
+    end
+  end
+
   describe 'clean_structure_sql' do
     let_it_be(:clean_rake_task) { 'gitlab:db:clean_structure_sql' }
     let_it_be(:test_task_name) { 'gitlab:db:_test_multiple_structure_cleans' }