Addon manager plugin support

Explain the feature

The Lua Language Server supports plugins that allow users to write custom Lua scripts that the language server will then run to output a modified file. As of right now, the addon manager will download the plugin.lua file, but it will not tell the server to use it. There should be some easy (and safe) way for users to enable a plugin that they have installed.

Are there any potential drawbacks from adding the feature?

There are some serious security concerns with downloading a script off the internet and running it automatically on the user's computer. While the addons being installed should be reviewed and trusted before being merged into LLS-addons, there is always the chance of something slipping through.

We could ask the user to review the code themselves before approving the request to enable it - but at the end of the day, the safest option will always be to not run code created by other users.

首先跟踪 addon manager 对下载的 plugin.lua 文件的处理方式，并查阅 LuaLS 关于 runtime.plugin 设置的文档。明确启用已安装插件所需的批准和安全要求，然后定义如何在不自动运行未经审查的代码的情况下验证完成情况。