Observable CORS for AWS Galaxy

On galaxy.hyphy.org, we service requests from `https://${USERNAME}.static.observableusercontent.com/` (where `${USERNAME}` is the user who owns the ObservableHQ notebook) in our NGINX logs. I think the corresponding edit for Apache would be something like:

```
Header set Access-Control-Allow-Origin "https://*.static.observableusercontent.com/"
Header set Access-Control-Allow-Methods "GET"
Header set Access-Control-Allow-Headers "DNT,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type,Range"
```

in `/etc/httpd/conf.d/galaxy.conf`.

Normally I’d just make this edit myself, check the configs (seems like `sudo httpd -t` for Apache) and restart the `httpd`. But since this is a (minor) security concern and it’s your system, I figured I’d run this by you and Dacian first.