The UpstreamConfig.Defaults field does not support setting Name or
Namespace because the purpose is to apply defaults to all upstreams.
I think this was just missed in the docs since those fields would
error if set under Defaults.
i.e. this is not supported:
```
UpstreamConfig {
Defaults {
Name = "foo"
Namespace = "bar"
# Defaults config here
}
}
```