VirtualHost metadata not merged with Route metadata

*Title*: *metadata from RouteConfiguration not merged into per-route metadata map*

*Description*:

I have a VirtualHost set up to contain metadata, as well as per-route metadata configured for each route. They both use the `envoy.filters.http.lua` namespace. However, inside the Lua handler, only the per-route metadata is available, not the one that I configured in the VirtualHost.

According to the documentation
> Metadata key-values for a filter are merged as connection and request handling occurs, with later values for the same key overriding earlier values.

but that seems to not be happening.

What am I doing wrong?

The obvious workaround for this would be to simply add the "top level" metadata to each route, but with over 600 routes, that is quite a lot of boilerplate.

Here is a minified excerpt from my configuration to illustrate the setup:

```yaml
- "@type": "type.googleapis.com/envoy.config.route.v3.RouteConfiguration"
name: "xds_routes"
virtual_hosts:
- domains:
- "*"
metadata:
filter_metadata:
envoy.filters.http.lua:
should_be_merged_in: "but it is not"
name: "xds_upstream"
routes:
- metadata:
filter_metadata:
envoy.filters.http.lua:
route_meta:
this_meatada: "can be accessed inside the lua handler"
```