webhooks: Convert gitlab to use @typed_endpoint.

The GitLab webhook has a mix of different types of parameters each
requring a unique set of configurations.

zerver/webhooks/gitlab/view.py

@@ -3,13 +3,15 @@ from functools import partial
 from typing import Dict, List, Optional, Protocol, Union
 
 from django.http import HttpRequest, HttpResponse
+from pydantic import Json
 
 from zerver.decorator import webhook_view
 from zerver.lib.exceptions import UnsupportedWebhookEventTypeError
-from zerver.lib.request import REQ, has_request_variables
 from zerver.lib.response import json_success
-from zerver.lib.validator import WildValue, check_bool, check_int, check_string, to_wild_value
+from zerver.lib.typed_endpoint import WebhookPayload, typed_endpoint
+from zerver.lib.validator import WildValue, check_int, check_string
 from zerver.lib.webhooks.common import (
+    OptionalUserSpecifiedTopicStr,
     check_send_webhook_message,
     validate_extract_webhook_http_header,
 )
@@ -416,14 +418,15 @@ ALL_EVENT_TYPES = list(EVENT_FUNCTION_MAPPER.keys())
 
 
 @webhook_view("GitLab", all_event_types=ALL_EVENT_TYPES)
-@has_request_variables
+@typed_endpoint
 def api_gitlab_webhook(
     request: HttpRequest,
     user_profile: UserProfile,
-    payload: WildValue = REQ(argument_type="body", converter=to_wild_value),
-    branches: Optional[str] = REQ(default=None),
-    use_merge_request_title: bool = REQ(default=True, json_validator=check_bool),
-    user_specified_topic: Optional[str] = REQ("topic", default=None),
+    *,
+    payload: WebhookPayload[WildValue],
+    branches: Optional[str] = None,
+    use_merge_request_title: Json[bool] = True,
+    user_specified_topic: OptionalUserSpecifiedTopicStr = None,
 ) -> HttpResponse:
     event = get_event(request, payload, branches)
     if event is not None: