添加安全DNS（DoH）开关设置项

[devnakx]

Acknowledgements / 确认事项

• I have updated to the latest version of the app / 已经更新到最新版
• I have tried the FAQ / 试过FAQ了. FAQ
• I have searched the existing issues and this is new ticket NOT a duplicate or related to another issue / 搜索过其他issue，确实不是重复问题
• I will fill out the title and the information in this template / 填好标题和内容

What feature should be added? / 需要加上什么功能

设置里找了一圈没有看到安全DNS（DoH）的开关配置项
目前 app 默认使用 Cloudflare DoH 进行查询
如在已是可信 DNS 的网络环境下没有必要再通过 DoH 进行查询
希望提供类似如下的设置项：

Official support / 官方支持情况

• Is this feature supported by the official pixiv app? / 官方App是否支持

Is this feature supported by any other third-party pixiv app? / 第三方App是否支持

No response

Any other information can be help? / 其它信息

No response