Use a background job to import accountability results

[ferblape]

🎩 User Story

Decidim Accountability module includes an importer of results. To make this importer more reliable it should be executed as a background process.

When the import finishes, the admin should be notified:

1. with the status of the process
2. in case of errors, which were the errors

Notice that this feedback is already implemented as part of the importer, and should be adapted to the new asynchronous implementation.

📋 Related documentation

None

🎯 Acceptance criteria

An admin should be able to import the current projects CSV (+4000 rows).

📌 Related issues

#189