Sanitise uploaded letters and store in S3

This sanitises uploaded letters and stores the sanitised result in S3
with if it passes validation or the original PDF in S3 if validation
fails. A metadata value of 'status' is set to either 'valid' or
'invalid'.

app/s3_client/s3_letter_upload_client.py

@@ -0,0 +1,16 @@
+from flask import current_app
+from notifications_utils.s3 import s3upload as utils_s3upload
+
+
+def get_transient_letter_file_location(service_id, upload_id):
+    return 'service-{}/{}.pdf'.format(service_id, upload_id)
+
+
+def upload_letter_to_s3(data, file_location, status):
+    utils_s3upload(
+        filedata=data,
+        region=current_app.config['AWS_REGION'],
+        bucket_name=current_app.config['TRANSIENT_UPLOADED_LETTERS'],
+        file_location=file_location,
+        metadata={'status': status}
+    )