Configuration reference documentation

## Documentation request

### Add a new page 🆕

**What documentation you'd like us to add?**

1. Add a reference for all (non-internal) configurable values for users.
1. Add a shortcode `<<% config value_name %>>` which creates an automatic label+link(+hoverbox?) to the reference whenever we use a config value in the documentation somewhere (for example scenarios page). Something like

```html

{{ .Params 0 }}
```

**Where in the documentation tree?**

A new section called "reference", or "Usage".