When redownloading images, ensure that renditions are recreated

...by deleting any local DB records related to them.

This basically wipes all renditions, which is fine for local dev as they
can be auto-created on the fly locally, unlike in prod

bedrock/cms/management/commands/download_media_to_local.py

@@ -79,7 +79,10 @@ def handle(self, *args, **options):
                 blob = bucket.blob(image_key)
                 blob.download_to_filename(local_dest)
                 self.stdout.write(f"Downloaded {image_key} from {bucket_name} to {local_dest}\n")
-
+                if redownload:
+                    # The DB will still think it has renditions included, and we want to regenerate those
+                    self.stdout.write(f"Deleting DB records of old renditions for {image_key}\n")
+                    image.renditions.all().delete()
                 image._pre_generate_expected_renditions()
                 self.stdout.write("Triggered local generation of renditions\n")