Use error.message instead of error in importer.log

Elasticsearch expects `error` to be an object representing the
exception. Rename the field to `error.message` to avoid parsing
conflicts.

app/services/projects/after_import_service.rb

@@ -26,7 +26,7 @@ module Projects
         message: 'Project housekeeping failed',
         project_full_path: @project.full_path,
         project_id: @project.id,
-        error: e.message
+        'error.message' => e.message
       )
     end
 

changelogs/unreleased/sh-update-importer-log-error-field.yml

+---
+title: Use error.message instead of error in importer.log
+merge_request: 36104
+author:
+type: fixed

spec/services/projects/after_import_service_spec.rb

@@ -72,6 +72,26 @@ RSpec.describe Projects::AfterImportService do
       end
     end
 
+    context 'when housekeeping service lease is taken' do
+      let(:exception) { Projects::HousekeepingService::LeaseTaken.new }
+
+      it 'logs the error message' do
+        allow_next_instance_of(Projects::HousekeepingService) do |instance|
+          expect(instance).to receive(:execute).and_raise(exception)
+        end
+
+        expect(Gitlab::Import::Logger).to receive(:info).with(
+          {
+            message: 'Project housekeeping failed',
+            project_full_path: project.full_path,
+            project_id: project.id,
+            'error.message' => exception.to_s
+          }).and_call_original
+
+        subject.execute
+      end
+    end
+
     context 'when after import action throw retriable exception one time' do
       let(:exception) { GRPC::DeadlineExceeded.new }