Look in organisation for whitelisted domains

At the moment we have to update a YAML file and deploy the change to get
a new domain whitelisted.

We already have a thing for adding new domains – the organisation stuff.

This commit extends the validation to look in the `domains` table on the
API if it can’t find anything in the YAML whitelist.

This has the advantage of:
- not having to deploy code to whitelist a new domain
- forcing us to create new organisations as they come along, so that
  users’ services automatically get allocated to the organisation once
  their domain is whitelisted

app/utils.py

@@ -31,6 +31,8 @@ from orderedset._orderedset import OrderedSet
 from werkzeug.datastructures import MultiDict
 from werkzeug.routing import RequestRedirect
 
+from app.notify_client.organisations_api_client import organisations_client
+
 SENDING_STATUSES = ['created', 'pending', 'sending', 'pending-virus-check']
 DELIVERED_STATUSES = ['delivered', 'sent', 'returned-letter']
 FAILURE_STATUSES = ['failed', 'temporary-failure', 'permanent-failure',
@@ -315,13 +317,21 @@ def get_help_argument():
     return request.args.get('help') if request.args.get('help') in ('1', '2', '3') else None
 
 
-def is_gov_user(email_address):
+def email_address_ends_with(email_address, known_domains):
     return any(
         email_address.lower().endswith((
             "@{}".format(known),
             ".{}".format(known),
         ))
-        for known in GOVERNMENT_EMAIL_DOMAIN_NAMES
+        for known in known_domains
+    )
+
+
+def is_gov_user(email_address):
+    return email_address_ends_with(
+        email_address, GOVERNMENT_EMAIL_DOMAIN_NAMES
+    ) or email_address_ends_with(
+        email_address, organisations_client.get_domains()
     )