Change function and task name to be more accurate

Will require us to change a cronitor set up

app/celery/letters_pdf_tasks.py

@@ -118,9 +118,9 @@ def get_letters_pdf(template, contact_block, filename, values):
     return resp.content, billable_units
 
 
-@notify_celery.task(name='collate-letter-pdfs-for-day')
-@cronitor("collate-letter-pdfs-for-day")
-def collate_letter_pdfs_for_day():
+@notify_celery.task(name='collate-letter-pdfs-to-be-sent')
+@cronitor("collate-letter-pdfs-to-be-sent")
+def collate_letter_pdfs_to_be_sent():
     """
     Finds all letters which are still waiting to be sent to DVLA for printing
 

app/config.py

@@ -296,8 +296,8 @@ class Config(object):
         },
         # The collate-letter-pdf does assume it is called in an hour that BST does not make a
         # difference to the truncate date which translates to the filename to process
-        'collate-letter-pdfs-for-day': {
-            'task': 'collate-letter-pdfs-for-day',
+        'collate-letter-pdfs-to-be-sent': {
+            'task': 'collate-letter-pdfs-to-be-sent',
             'schedule': crontab(hour=17, minute=50),
             'options': {'queue': QueueNames.PERIODIC}
         },