add content to broadcast_message and make template fields nullable

we want to be able to create broadcast messages without templates. To
start with, these will come from the API, but in future we may want to
let people create via the admin interface without creating a template
too.

populate a non-nullable content field with the values supplied via the
template (or supplied directly if via api).

tests/app/db.py

@@ -2,6 +2,8 @@ import random
 import uuid
 from datetime import datetime, date, timedelta
 
+import pytest
+
 from app import db
 from app.dao.email_branding_dao import dao_create_email_branding
 from app.dao.inbound_sms_dao import dao_create_inbound_sms
@@ -1010,24 +1012,44 @@ def create_service_contact_list(
 
 
 def create_broadcast_message(
-    template,
+    template=None,
+    *,
+    service=None,  # only used if template is not provided
     created_by=None,
     personalisation=None,
+    content=None,
     status=BroadcastStatusType.DRAFT,
     starts_at=None,
     finishes_at=None,
     areas=None,
 ):
+    if template:
+        service = template.service
+        template_id = template.id
+        template_version = template.version
+        personalisation = personalisation or {}
+        content = template._as_utils_template_with_personalisation(
+            personalisation
+        ).content_with_placeholders_filled_in
+    elif content:
+        template_id = None
+        template_version = None
+        personalisation = None
+        content = content
+    else:
+        pytest.fail('Provide template or content')
+
     broadcast_message = BroadcastMessage(
-        service_id=template.service_id,
-        template_id=template.id,
-        template_version=template.version,
-        personalisation=personalisation or {},
+        service_id=service.id,
+        template_id=template_id,
+        template_version=template_version,
+        personalisation=personalisation,
         status=status,
         starts_at=starts_at,
         finishes_at=finishes_at,
-        created_by_id=created_by.id if created_by else template.created_by_id,
+        created_by_id=created_by.id if created_by else service.created_by_id,
         areas=areas or {},
+        content=content
     )
     db.session.add(broadcast_message)
     db.session.commit()