[API] Add pagination to ListBranches (#14524)

* make PaginateUserSlice generic -> PaginateSlice

* Add pagination to ListBranches

* add skip, limit to Repository.GetBranches()

* Move routers/api/v1/utils/utils PaginateSlice -> modules/util/paginate.go

* repo_module.GetBranches paginate

* fix & rename & more logging

* better description

Co-authored-by: zeripath <art27@cantab.net>
Co-authored-by: a1012112796 <1012112796@qq.com>

modules/util/paginate.go

@@ -0,0 +1,34 @@
+// Copyright 2021 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package util
+
+import "reflect"
+
+// PaginateSlice cut a slice as per pagination options
+// if page = 0 it do not paginate
+func PaginateSlice(list interface{}, page, pageSize int) interface{} {
+	if page <= 0 || pageSize <= 0 {
+		return list
+	}
+	if reflect.TypeOf(list).Kind() != reflect.Slice {
+		return list
+	}
+
+	listValue := reflect.ValueOf(list)
+
+	page--
+
+	if page*pageSize >= listValue.Len() {
+		return listValue.Slice(listValue.Len(), listValue.Len()).Interface()
+	}
+
+	listValue = listValue.Slice(page*pageSize, listValue.Len())
+
+	if listValue.Len() > pageSize {
+		return listValue.Slice(0, pageSize).Interface()
+	}
+
+	return listValue.Interface()
+}