Allow setting up logging level in core loader

This will allow bumping the verbosity level when debugging some loaders. And actually lowering the current verbosity on existing loaders (e.g. cvs one) without losing the possibility to be more verbose in debugging mode.

Related to swh-core#4229

---

Migrated from D7805 (view on Phabricator)

swh/loader/core/loader.py

@@ -87,6 +87,7 @@ class BaseLoader:
         lister_name: Optional[str] = None,
         lister_instance_name: Optional[str] = None,
         metadata_fetcher_credentials: CredentialsType = None,
+        **kwargs,
     ):
         if lister_name == "":
             raise ValueError("lister_name must not be the empty string")
@@ -116,6 +117,9 @@ class BaseLoader:
         _log = logging.getLogger("requests.packages.urllib3.connectionpool")
         _log.setLevel(logging.WARN)
 
+        self.log.setLevel(
+            logging.DEBUG if kwargs.get("debug") is True else logging.INFO
+        )
         # possibly overridden in self.prepare method
         self.visit_date = datetime.datetime.now(tz=datetime.timezone.utc)