objstorage_checker: Add support for consuming content ids from journal

Add ObjectStorageCheckerJournal class to consume content ids from a kafka topic in order to check their presence in a given object storage but also to check their integrity by fetching their bytes and recomputing checksums.

Related to #4694 (closed).

swh/scrubber/objstorage_checker.py

@@ -125,7 +125,7 @@ class ObjectStorageCheckerPartition(BasePartitionChecker):
 
 
 class ObjectStorageCheckerJournal(BaseChecker):
-    """A jourbal based checker to detect missing and corrupted contents in an object storage.
+    """A journal based checker to detect missing and corrupted contents in an object storage.
 
     It iterates on content objects referenced in a kafka topic, check they are available
     in a given object storage instance then retrieve their bytes from it in order to