Fix celery configuration not being applied sometimes

The module dispatching the celery tasks did not import
our celery worker module, which resulted in the celery configuration not
being applied in some cases, e.g. when using uvicorn's hot reload
functionality.

By referencing the celery tasks directly, we make sure that the celery
config used for defining the tasks is also used for dispatching them.

See https://docs.celeryq.dev/en/stable/userguide/application.html#breaking-the-chain
for more information.

backend/src/app/celery/background_jobs/__init__.py

@@ -2,53 +2,36 @@
 from typing import Any, List
 
 # noinspection PyUnresolvedReferences,PyProtectedMember
-from celery.canvas import Signature
-
+from app.celery.background_jobs.tasks import (
+    execute_audio_preprocessing_pipeline_task,
+    execute_image_preprocessing_pipeline_task,
+    execute_text_preprocessing_pipeline_task,
+    execute_video_preprocessing_pipeline_task,
+    import_uploaded_archive,
+    start_crawler_job,
+    start_export_job,
+)
 from app.core.data.crawler.crawler_service import CrawlerService
 from app.core.data.dto.crawler_job import CrawlerJobParameters, CrawlerJobRead
 from app.core.data.dto.export_job import ExportJobParameters, ExportJobRead
 from app.core.data.export.export_service import ExportService
 from app.preprocessing.pipeline.model.pipeline_cargo import PipelineCargo
 
-import_uploaded_archive_task = (
-    "app.celery.background_jobs.tasks.import_uploaded_archive"
-)
-start_export_job_task = "app.celery.background_jobs.tasks.start_export_job"
-start_crawler_job_task = "app.celery.background_jobs.tasks.start_crawler_job"
-
-execute_text_preprocessing_pipeline_task = (
-    "app.celery.background_jobs.tasks.execute_text_preprocessing_pipeline_task"
-)
-execute_image_preprocessing_pipeline_task = (
-    "app.celery.background_jobs.tasks.execute_image_preprocessing_pipeline_task"
-)
-execute_audio_preprocessing_pipeline_task = (
-    "app.celery.background_jobs.tasks.execute_audio_preprocessing_pipeline_task"
-)
-execute_video_preprocessing_pipeline_task = (
-    "app.celery.background_jobs.tasks.execute_video_preprocessing_pipeline_task"
-)
-
 
 def import_uploaded_archive_apply_async(
     archive_file_path: Path, project_id: int
 ) -> Any:
-    archive_preprocessing = Signature(
-        import_uploaded_archive_task,
+    return import_uploaded_archive.apply_async(
         kwargs={"archive_file_path_and_project_id": (archive_file_path, project_id)},
     )
-    return archive_preprocessing.apply_async()
 
 
 def prepare_and_start_export_job_async(
     export_params: ExportJobParameters,
 ) -> ExportJobRead:
     exs: ExportService = ExportService()
     ex_job = exs.prepare_export_job(export_params)
-    start_export_job = Signature(start_export_job_task, kwargs={"export_job": ex_job})
-    start_export_job.apply_async()
-
-    return ex_job
+    return start_export_job.apply_async(kwargs={"export_job": ex_job})
 
 
 def prepare_and_start_crawling_job_async(
@@ -58,11 +41,11 @@ def prepare_and_start_crawling_job_async(
     cj = cs.prepare_crawler_job(crawler_params)
     start_export_job = (
         # crawl the data via scrapy and zip the data
-        Signature(start_crawler_job_task, kwargs={"crawler_job": cj})
+        start_crawler_job.signature(kwargs={"crawler_job": cj})
         |
         # import the zip
         # TODO create a PPJ for the import
-        Signature(import_uploaded_archive_task)
+        import_uploaded_archive.signature()
     )
     start_export_job.apply_async()
 
@@ -73,33 +56,25 @@ def execute_text_preprocessing_pipeline_apply_async(
     cargos: List[PipelineCargo],
 ) -> None:
     for cargo in cargos:
-        Signature(
-            execute_text_preprocessing_pipeline_task, kwargs={"cargo": cargo}
-        ).apply_async()
+        execute_text_preprocessing_pipeline_task.apply_async(kwargs={"cargo": cargo})
 
 
 def execute_image_preprocessing_pipeline_apply_async(
     cargos: List[PipelineCargo],
 ) -> None:
     for cargo in cargos:
-        Signature(
-            execute_image_preprocessing_pipeline_task, kwargs={"cargo": cargo}
-        ).apply_async()
+        execute_image_preprocessing_pipeline_task.apply_async(kwargs={"cargo": cargo})
 
 
 def execute_audio_preprocessing_pipeline_apply_async(
     cargos: List[PipelineCargo],
 ) -> None:
     for cargo in cargos:
-        Signature(
-            execute_audio_preprocessing_pipeline_task, kwargs={"cargo": cargo}
-        ).apply_async()
+        execute_audio_preprocessing_pipeline_task.apply_async(kwargs={"cargo": cargo})
 
 
 def execute_video_preprocessing_pipeline_apply_async(
     cargos: List[PipelineCargo],
 ) -> None:
     for cargo in cargos:
-        Signature(
-            execute_video_preprocessing_pipeline_task, kwargs={"cargo": cargo}
-        ).apply_async()
+        execute_video_preprocessing_pipeline_task.apply_async(kwargs={"cargo": cargo})