Add a simple way to rename branch like gh (#15870)

- Update default branch if needed
- Update protected branch if needed
- Update all not merged pull request base branch name
- Rename git branch
- Record this rename work and auto redirect for old branch on ui

Signed-off-by: a1012112796 <1012112796@qq.com>
Co-authored-by: delvh <dev.lh@web.de>

services/repository/branch.go

@@ -10,10 +10,49 @@ import (
 	"code.gitea.io/gitea/models"
 	"code.gitea.io/gitea/modules/git"
 	"code.gitea.io/gitea/modules/log"
+	"code.gitea.io/gitea/modules/notification"
 	repo_module "code.gitea.io/gitea/modules/repository"
 	pull_service "code.gitea.io/gitea/services/pull"
 )
 
+// RenameBranch rename a branch
+func RenameBranch(repo *models.Repository, doer *models.User, gitRepo *git.Repository, from, to string) (string, error) {
+	if from == to {
+		return "target_exist", nil
+	}
+
+	if gitRepo.IsBranchExist(to) {
+		return "target_exist", nil
+	}
+
+	if !gitRepo.IsBranchExist(from) {
+		return "from_not_exist", nil
+	}
+
+	if err := repo.RenameBranch(from, to, func(isDefault bool) error {
+		err2 := gitRepo.RenameBranch(from, to)
+		if err2 != nil {
+			return err2
+		}
+
+		if isDefault {
+			err2 = gitRepo.SetDefaultBranch(to)
+			if err2 != nil {
+				return err2
+			}
+		}
+
+		return nil
+	}); err != nil {
+		return "", err
+	}
+
+	notification.NotifyDeleteRef(doer, repo, "branch", "refs/heads/"+from)
+	notification.NotifyCreateRef(doer, repo, "branch", "refs/heads/"+to)
+
+	return "", nil
+}
+
 // enmuerates all branch related errors
 var (
 	ErrBranchIsDefault   = errors.New("branch is default")