Extract template / csv utility code into modules

This follows a similar approach to the previous commits, noting that
one module depends on the other, so we have to extract both together.

app/models/contact_list.py

@@ -16,7 +16,7 @@ from app.s3_client.s3_csv_client import (
     s3upload,
     set_metadata_on_csv_upload,
 )
-from app.utils import get_sample_template
+from app.utils.templates import get_sample_template
 
 
 class ContactList(JSONModel):