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/user/user.go

@@ -20,6 +20,7 @@ import (
 	"code.gitea.io/gitea/modules/auth/openid"
 	"code.gitea.io/gitea/modules/auth/password/hash"
 	"code.gitea.io/gitea/modules/base"
+	"code.gitea.io/gitea/modules/container"
 	"code.gitea.io/gitea/modules/git"
 	"code.gitea.io/gitea/modules/log"
 	"code.gitea.io/gitea/modules/setting"
@@ -910,6 +911,15 @@ func GetUserByID(ctx context.Context, id int64) (*User, error) {
 	return u, nil
 }
 
+// GetUserByIDs returns the user objects by given IDs if exists.
+func GetUserByIDs(ctx context.Context, ids []int64) ([]*User, error) {
+	users := make([]*User, 0, len(ids))
+	err := db.GetEngine(ctx).In("id", ids).
+		Table("user").
+		Find(&users)
+	return users, err
+}
+
 // GetPossibleUserByID returns the user if id > 0 or return system usrs if id < 0
 func GetPossibleUserByID(ctx context.Context, id int64) (*User, error) {
 	switch id {
@@ -924,6 +934,25 @@ func GetPossibleUserByID(ctx context.Context, id int64) (*User, error) {
 	}
 }
 
+// GetPossibleUserByIDs returns the users if id > 0 or return system users if id < 0
+func GetPossibleUserByIDs(ctx context.Context, ids []int64) ([]*User, error) {
+	uniqueIDs := container.SetOf(ids...)
+	users := make([]*User, 0, len(ids))
+	_ = uniqueIDs.Remove(0)
+	if uniqueIDs.Remove(-1) {
+		users = append(users, NewGhostUser())
+	}
+	if uniqueIDs.Remove(ActionsUserID) {
+		users = append(users, NewActionsUser())
+	}
+	res, err := GetUserByIDs(ctx, uniqueIDs.Values())
+	if err != nil {
+		return nil, err
+	}
+	users = append(users, res...)
+	return users, nil
+}
+
 // GetUserByNameCtx returns user by given name.
 func GetUserByName(ctx context.Context, name string) (*User, error) {
 	if len(name) == 0 {