Add worker to export projects in parallel

What does this MR do and why?

This change is part of a sequence of changes that will export projects using multiple Sidekiq Jobs rather than running the whole export process in just one single job.

This MR adds the worker and service responsible for generating the final project export archive, uploading the file to object store, and notifying the user that the project was exported.

The worker and service are similar to the ProjectExportWorker and Projects::ImportExport::ExportService, and because of that, they share most of the same components.

For context, Projects::ImportExport::ExportService uses several "savers" classes to export each relation of the project and put them in a folder that is compressed in a tar.gz file. On the other hand, ParallelExportService uses ExportedRelationsMerger class (introduced in !102815 (merged)) to merge all relations that are exported in parallel into a folder that is compressed in a tar.gz file.

Related to: #360685 (closed)

Screenshots or screen recordings

parallel-export

How to set up and validate locally

Because this is a work in progress, the Rails console needs to be used to test the change.

Open the Rails console and execute the commands below. The commands will enqueue several Sidekiq Jobs, and each will export a relation of the project and upload/copy the file to object store.

In the table project_export_jobs and project_relation_export_uploads it's possible to check when the export completes.

project = Project.first # pick a project to export

project_export_job = project.export_jobs.create(status: 0, jid: SecureRandom.hex(10))

Projects::ImportExport::RelationExport.relation_names_list.each do |relation|
  relation_export = project_export_job.relation_exports.create(relation: relation)
  Projects::ImportExport::RelationExportWorker.perform_async(relation_export.id)
end

project_export_job.start!

When all relations are exported, use the command below to execute the worker that will compress the exported files, generate a tar.gz, upload to object store, and notify the user.

Projects::ImportExport::ParallelProjectExportWorker.perform_async(project_export_job.id, User.first.id)

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

app/services/projects/import_export/parallel_export_service.rb

@@ -12,10 +12,10 @@ def initialize(export_job, current_user, after_export_strategy)
       end
 
       def execute
-        log_info('Project export started')
+        log_info('Parallel project export started')
 
         if save_exporters && save_export_archive
-          log_info('Project successfully exported')
+          log_info('Parallel project export finished successfully')
           execute_after_export_action(after_export_strategy)
         else
           notify_error
@@ -77,7 +77,7 @@ def log_info(message)
 
       def notify_error
         logger.error(
-          message: 'Project export error',
+          message: 'Parallel project export error',
           export_errors: shared.errors.join(', '),
           export_job_id: export_job.id,
           **log_base_data