Implement update branch API (#32433)

Resolves #22526.

Builds upon #23061.

---------

Co-authored-by: sillyguodong <33891828+sillyguodong@users.noreply.github.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

routers/api/v1/repo/branch.go

@@ -386,6 +386,77 @@ func ListBranches(ctx *context.APIContext) {
 	ctx.JSON(http.StatusOK, apiBranches)
 }
 
+// UpdateBranch updates a repository's branch.
+func UpdateBranch(ctx *context.APIContext) {
+	// swagger:operation PATCH /repos/{owner}/{repo}/branches/{branch} repository repoUpdateBranch
+	// ---
+	// summary: Update a branch
+	// consumes:
+	// - application/json
+	// produces:
+	// - application/json
+	// parameters:
+	// - name: owner
+	//   in: path
+	//   description: owner of the repo
+	//   type: string
+	//   required: true
+	// - name: repo
+	//   in: path
+	//   description: name of the repo
+	//   type: string
+	//   required: true
+	// - name: branch
+	//   in: path
+	//   description: name of the branch
+	//   type: string
+	//   required: true
+	// - name: body
+	//   in: body
+	//   schema:
+	//     "$ref": "#/definitions/UpdateBranchRepoOption"
+	// responses:
+	//   "204":
+	//     "$ref": "#/responses/empty"
+	//   "403":
+	//     "$ref": "#/responses/forbidden"
+	//   "404":
+	//     "$ref": "#/responses/notFound"
+	//   "422":
+	//     "$ref": "#/responses/validationError"
+
+	opt := web.GetForm(ctx).(*api.UpdateBranchRepoOption)
+
+	oldName := ctx.PathParam("*")
+	repo := ctx.Repo.Repository
+
+	if repo.IsEmpty {
+		ctx.Error(http.StatusNotFound, "", "Git Repository is empty.")
+		return
+	}
+
+	if repo.IsMirror {
+		ctx.Error(http.StatusForbidden, "", "Git Repository is a mirror.")
+		return
+	}
+
+	msg, err := repo_service.RenameBranch(ctx, repo, ctx.Doer, ctx.Repo.GitRepo, oldName, opt.Name)
+	if err != nil {
+		ctx.Error(http.StatusInternalServerError, "RenameBranch", err)
+		return
+	}
+	if msg == "target_exist" {
+		ctx.Error(http.StatusUnprocessableEntity, "", "Cannot rename a branch using the same name or rename to a branch that already exists.")
+		return
+	}
+	if msg == "from_not_exist" {
+		ctx.Error(http.StatusNotFound, "", "Branch doesn't exist.")
+		return
+	}
+
+	ctx.Status(http.StatusNoContent)
+}
+
 // GetBranchProtection gets a branch protection
 func GetBranchProtection(ctx *context.APIContext) {
 	// swagger:operation GET /repos/{owner}/{repo}/branch_protections/{name} repository repoGetBranchProtection