alert_words: Update add_alert_words codepath to send event on commit.

Earlier, we were using 'send_event' in 'do_add_alert_words' which
can lead to a situation, if any db operation is added after the
'send_event' in future, where we enqueue events but the action
function fails at a later stage.

Events should not be sent until we know we're not rolling back.

Fixes part of #30489.

zerver/actions/alert_words.py

@@ -1,15 +1,18 @@
 from collections.abc import Iterable, Sequence
 
+from django.db import transaction
+
 from zerver.lib.alert_words import add_user_alert_words, remove_user_alert_words
 from zerver.models import UserProfile
-from zerver.tornado.django_api import send_event
+from zerver.tornado.django_api import send_event_on_commit
 
 
 def notify_alert_words(user_profile: UserProfile, words: Sequence[str]) -> None:
     event = dict(type="alert_words", alert_words=words)
-    send_event(user_profile.realm, event, [user_profile.id])
+    send_event_on_commit(user_profile.realm, event, [user_profile.id])
 
 
+@transaction.atomic(savepoint=False)
 def do_add_alert_words(user_profile: UserProfile, alert_words: Iterable[str]) -> None:
     words = add_user_alert_words(user_profile, alert_words)
     notify_alert_words(user_profile, words)

zerver/lib/alert_words.py

@@ -50,7 +50,7 @@ def user_alert_words(user_profile: UserProfile) -> list[str]:
     return list(AlertWord.objects.filter(user_profile=user_profile).values_list("word", flat=True))
 
 
-@transaction.atomic
+@transaction.atomic(savepoint=False)
 def add_user_alert_words(user_profile: UserProfile, new_words: Iterable[str]) -> list[str]:
     existing_words_lower = {word.lower() for word in user_alert_words(user_profile)}