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/issues/review.go

@@ -162,6 +162,27 @@ func (r *Review) LoadReviewer(ctx context.Context) (err error) {
 	return err
 }
 
+// LoadReviewers loads reviewers
+func LoadReviewers(ctx context.Context, reviews []*Review) (err error) {
+	reviewerIds := make([]int64, len(reviews))
+	for i := 0; i < len(reviews); i++ {
+		reviewerIds[i] = reviews[i].ReviewerID
+	}
+	reviewers, err := user_model.GetPossibleUserByIDs(ctx, reviewerIds)
+	if err != nil {
+		return err
+	}
+
+	userMap := make(map[int64]*user_model.User, len(reviewers))
+	for _, reviewer := range reviewers {
+		userMap[reviewer.ID] = reviewer
+	}
+	for _, review := range reviews {
+		review.Reviewer = userMap[review.ReviewerID]
+	}
+	return nil
+}
+
 // LoadReviewerTeam loads reviewer team
 func (r *Review) LoadReviewerTeam(ctx context.Context) (err error) {
 	if r.ReviewerTeamID == 0 || r.ReviewerTeam != nil {
@@ -520,8 +541,8 @@ func GetReviews(ctx context.Context, opts *GetReviewOptions) ([]*Review, error)
 	return reviews, sess.Find(&reviews)
 }
 
-// GetReviewersByIssueID gets the latest review of each reviewer for a pull request
-func GetReviewersByIssueID(issueID int64) ([]*Review, error) {
+// GetReviewsByIssueID gets the latest review of each reviewer for a pull request
+func GetReviewsByIssueID(issueID int64) ([]*Review, error) {
 	reviews := make([]*Review, 0, 10)
 
 	sess := db.GetEngine(db.DefaultContext)