vscode: add the "clean", "unit test" and "code sytle check" tasks in the file: "./vscode/tasks.json" and improve the corresponding help document file: "docs/howto/how_to_build_and_release.md". A small bug is also fixed in the "start_build_docker" function of the file "apollo_docker.sh" when using vscode to pull the docker image from China.   (#3309)

* vscode: add the "clean" and "code sytle check" tasks in the file: "./vscode/tasks.json" and improve the corresponding help document file: "docs/howto/how_to_build_and_release.md". A small bug is also fixed in the "start_build_docker" function of the file "apollo_docker.sh" when using vscode to pull the docker image from China.

docs: change how_to_build_and_release.md in order to add contents on "build_in_vscode" and apollo_docker.sh: fetch the docker image with different method (#3041)

*  Add the "apollo/dev_build.sh" and "apollo/.vscode/tasks.json" files to build the Apollo project in VSCode.

* replace "dev_build.sh" with "apollo_docker.sh " and "dev_build.sh" is no longer needed.

* apollo_docker.sh: fetch the docker image with different  method.

* docs: add build_in_vscode documents in how_to_build_and_release.md