docs: add proxy_opts attribute for openid-connect.md (#9922)

[darkSheep404]

Description

update openid-connect docs, add attribute proxy-opts,which enable openid-connect access oauth2 server with http-proxy sever
更新openid-connect 文档 添加属性 proxy-opts,通过配置此属性 可以使得openid-connect 使用代理服务器访问 配置的oauth2服务器
Fixes # (issue)
#9922

hi @Sn0rt

Can you please help me to review this PR
After our last discussion, by reading the openid-connect.lua and openidc.lua source code I found the available configuration items and tested them in my online environment
If there is no problem, I will update it to the document the LTS version too.
But there seems to be no better way for me to update all the documentation at once than to give each release a PR

你可以帮我review这个PR吗
在我们上次讨论之后 通过阅读openid-connet与openid的源码 我找到了可用的配置项,并且在我的线上环测试过是可行的
如果没问题的话 我会再把它更新到LTS版本的文档
不过似乎我没有更好的方式去一次性更新所有文档 除了给每个版本都提一次PR

Here is a simple diagram,the plugin config of openid-connect will be passed to openidc.lua as opts,and will be used to set_proxy_options
这里是一个简单的图,openid-connect 插件的配置 将会被传递给 openidc.lua文件作为opts,并被用来 指定代理服务器

    if httpc and proxy_opts and type(proxy_opts) == "table" then
        log(DEBUG, "openidc_configure_proxy : use http proxy")
        httpc:set_proxy_options(proxy_opts)
    else
        log(DEBUG, "openidc_configure_proxy : don't use http proxy")
    end
end

Checklist

• I have explained the need for this PR and the problem it solves
• I have explained the changes or the new features added to this PR
• I have added tests corresponding to this change
• I have updated the documentation to reflect this change
• I have verified that this change is backward compatible (If not, please discuss on the APISIX mailing list first)

[darkSheep404]

by the way,this pr only add a proxy_opts attribute to doc,if use git tools which can ignore format and emptylines will be more clearly,The indentation above is affected because markdown's table has been modified by adding a new line

捎带说一下 这个PR 其实只加了一个属性到文档,如果使用忽略格式化和空行的git 工具可以更清晰的看到更改. 因为修改了markdown的table,加了一行 所以影响到了上面的缩进