Add SSL support. 增加Node.js 自带的SSL 配置功能

[pingmoogle]

Feature request

What problem does this feature solve?

在VPS上使用vuepress，找不到证书的配置参数
when using vuepress on my VPS, I can't find how to config my certfications.

What does the proposed API look like?

在config.js 内添加ca、cert等参数支持
add CA, cert supports in config.js

How should this be implemented in your opinion?

在dev进行时，配置web服务器之前，检查证书配置
during 'vuepress dev' operation, check cert configuration in node.js app.js file

Are you willing to work on this yourself?

perhaps not