Add license header for source code

[yibin87]

For all files in tiflash root folder and descend folders(except contrib):

1. c/c++ .h/.cpp/.cc/.c file;
2. cmake file file(CMakeLists.txt and .cmake files);
3. python file(include init.py, refer to one Microsoft github tutel ); SheBang handled
4. bash file; SheBang handled
5. test files under tests folder
6. toml/yaml files
7. .s assemble files
   will add license header:

// Copyright 2022 PingCAP, Ltd.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

Files already added license header in release-centos7-llvm, will be updated.

Not handled file types:
clang related
git related
.md
json files
.in files that with comment "auto generated by cmake"
txt reference files
files with no ext and no SheBang