A brief description of the purpose of the changes contained in this PR.

Make the orphan files deletion task asynchronous. This comes with few changes to make it possible:

Enable the backend results of the celery tasks. This allows to store the states of any celery tasks. We use this to check is the task is running or not
upgrade the celery package to the closest version that fixes a known bug on incompatible version with python 3.9 that manifests only when working with celery task results
Fixes the patch number of the python version in the Dockerfile to match the one in the pyproject.toml file (else poetry won't be happy)
Add an API route to check the status of the orphan files deletion task
Update the frontend to reflect the status of the deletion task

For testing

Do not forget to build the docker images !