actions: Use transaction.atomic for do_add_linkifier.

This commit also renames the legacy event variable to
legacy_event from event because same event is sent
twice if we keep only single variable and change its
value. This was happening because the event value was
changed when the first send_event was actually executed.

zerver/actions/realm_linkifiers.py

@@ -1,6 +1,7 @@
 from typing import Dict, List, Optional
 
 import orjson
+from django.db import transaction
 from django.utils.timezone import now as timezone_now
 
 from zerver.lib.types import LinkifierDict
@@ -18,20 +19,21 @@ from zerver.tornado.django_api import send_event
 
 def notify_linkifiers(realm: Realm, realm_linkifiers: List[LinkifierDict]) -> None:
     event: Dict[str, object] = dict(type="realm_linkifiers", realm_linkifiers=realm_linkifiers)
-    send_event(realm, event, active_user_ids(realm.id))
+    transaction.on_commit(lambda: send_event(realm, event, active_user_ids(realm.id)))
 
     # Below is code for backwards compatibility. The now deprecated
     # "realm_filters" event-type is used by older clients, and uses
     # tuples.
     realm_filters = realm_filters_for_realm(realm.id)
-    event = dict(type="realm_filters", realm_filters=realm_filters)
-    send_event(realm, event, active_user_ids(realm.id))
+    legacy_event = dict(type="realm_filters", realm_filters=realm_filters)
+    transaction.on_commit(lambda: send_event(realm, legacy_event, active_user_ids(realm.id)))
 
 
 # NOTE: Regexes must be simple enough that they can be easily translated to JavaScript
 # RegExp syntax. In addition to JS-compatible syntax, the following features are available:
 #   * Named groups will be converted to numbered groups automatically
 #   * Inline-regex flags will be stripped, and where possible translated to RegExp-wide flags
+@transaction.atomic(durable=True)
 def do_add_linkifier(
     realm: Realm, pattern: str, url_format_string: str, *, acting_user: Optional[UserProfile]
 ) -> int: