Support for download and initialization of Mono

What does this MR do and why?

Resolved https://jihulab.com/gitlab-cn/gitlab/-/issues/3153

完成 Mono 的安装和初始化功能。同时完成此仓库的基础配置，包括 CI/CD、.gitignore 等。

PS: Mono 是基于 Google Repo，实现一个支持多仓管理的客户端工具。

Screenshots or screen recordings

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

How to set up and validate locally

See: 如何下载 Mono client，并在本地初始化

注意：安装步骤的 Mono 路径需要临时改一下：把 main-jh 改为 init-jihu-config，因为 main-jh 分支此时还没有合入新代码。

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.