New webhook trigger for receiving Pull Request review requests (#24481)

close https://github.com/go-gitea/gitea/issues/16321

Provided a webhook trigger for requesting someone to review the Pull
Request.

Some modifications have been made to the returned `PullRequestPayload`
based on the GitHub webhook settings, including:
- add a description of the current reviewer object as
`RequestedReviewer` .
- setting the action to either **review_requested** or
**review_request_removed** based on the operation.
- adding the `RequestedReviewers` field to the issues_model.PullRequest.
This field will be loaded into the PullRequest through
`LoadRequestedReviewers()` when `ToAPIPullRequest` is called.

After the Pull Request is merged, I will supplement the relevant
documentation.

models/webhook/webhook.go

@@ -298,6 +298,12 @@ func (w *Webhook) HasPackageEvent() bool {
 		(w.ChooseEvents && w.HookEvents.Package)
 }
 
+// HasPullRequestReviewRequestEvent returns true if hook enabled pull request review request event.
+func (w *Webhook) HasPullRequestReviewRequestEvent() bool {
+	return w.SendEverything ||
+		(w.ChooseEvents && w.HookEvents.PullRequestReviewRequest)
+}
+
 // EventCheckers returns event checkers
 func (w *Webhook) EventCheckers() []struct {
 	Has  func() bool
@@ -329,6 +335,7 @@ func (w *Webhook) EventCheckers() []struct {
 		{w.HasRepositoryEvent, webhook_module.HookEventRepository},
 		{w.HasReleaseEvent, webhook_module.HookEventRelease},
 		{w.HasPackageEvent, webhook_module.HookEventPackage},
+		{w.HasPullRequestReviewRequestEvent, webhook_module.HookEventPullRequestReviewRequest},
 	}
 }