Grab metadata when getting pdf letter preview from S3

Also use this metadata to decide whether preview pages need
overlay or not. So far we have always added overlay when validation
has failed. Now we will only show it when validation failed due to
content being outside of printable area.

app/letters/utils.py

@@ -164,7 +164,7 @@ def get_file_names_from_error_bucket():
     return bucket.objects.filter(Prefix="ERROR")
 
 
-def get_letter_pdf(notification):
+def get_letter_pdf_and_metadata(notification):
     bucket_name, prefix = get_bucket_name_and_prefix_for_notification(notification)
 
     s3 = boto3.resource('s3')
@@ -174,8 +174,8 @@ def get_letter_pdf(notification):
     obj = s3.Object(
         bucket_name=bucket_name,
         key=item.key
-    )
-    return obj.get()["Body"].read()
+    ).get()
+    return obj["Body"].read(), obj["Metadata"]
 
 
 def _move_s3_object(source_bucket, source_filename, target_bucket, target_filename, metadata=None):