Default varnish configurable

The varnish container comes with some default configurations.

For example in 'defaults/vcl_recv.vcl' the following code blocks any XMLHttpRequests from being cached.
```
# Do not cache ajax requests.
if (req.http.X-Requested-With == "XMLHttpRequest") {
set req.http.X-VC-Cacheable = "NO:Requested with: XMLHttpRequest";
return(pass);
}
```

Since this is executed before the 'lando.vcl', it seems like it is not possible to override this.

Do you think that there could be a way to override these defaults-files?
On the production server this is no issue, since I can just edit the files there. But in a container that's not really a possibility.

Start by inspecting defaults/vcl_recv.vcl and lando.vcl, then trace how the container loads these VCL files and in what order. Determine whether the default rules can be overridden through the existing configuration path; done means users can customize the defaults without editing files inside the container.

Written by the indexing model from the issue text.