Spec out API response for get modules endpoint

Example:
```
display_name: code-server
description: VS Code in the browser
icon: ../.icons/code.svg
maintainer_github: coder
verified: true
tags: [helper, ide, web]
```

```
// generated source code
type ModuleData struct {
Name string
CodeSnippet string
}

var APIResponses = []ModuleData{
{
Name: "hey",
CodeSnippet: "my code",
},
}

// normal source code
func (s Server) listModules() {
api.Write(APIResponses)
}
```

Plus the code snippet data from https://github.com/coder/internal/issues/412

This should be a shared struct that will both be used when parsing readmes and will be served from the API.