lib part of Gitee import (Gitee import 1/4)

What does this MR do and why?

Related to issue https://jihulab.com/gitlab-cn/gitlab/-/issues/1521.

This MR added lib part of Gitee import feature.

├── client.rb                    # 导入的 client，里边声明了获取各个资源的 URL，使用 personal_access_token 做权限校验
├── collection.rb                # 使用 Enumerator 分页获取资源
├── connection.rb                # 发送 api 请求的类
├── error
│   └── unauthorized.rb          
├── page.rb                      # Page 类，用于解析每页的数据，在 Paginator 类中使用
├── paginator.rb                 # 分页类，使用 items 分页获取数据
└── representation               # 对接口返回的数据进行序列化的目录
    ├── base.rb
    ├── label.rb
    ├── milestone.rb
    ├── issue_comment.rb
    ├── issue.rb
    ├── pull_request.rb
    ├── pull_request_comment.rb
    ├── repo.rb
    └── user.rb

How to use

client = Gitee::Client.new(gitee_access_token: '')

# get repos
client.repos.to_a

# get repo
client.repo(repo_name)

# get issues
client.issues(repo_name)

# get issue comments
client.issue_comments(repo_name, issue_number)

# get PRs
client.pull_requests(repo_name)

# get PR comments
client.pull_request_comments(repo_name, pull_request_number)

# get labels
client.labels(repo_name)

# get milestones
client.milestones(repo_name)

# get user info
client.user

Screenshots or screen recordings

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How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

MR acceptance checklist

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