[nginx] Experiment with table-based server blocks

allow config like:

```toml
[[http.servers]]
name = "foo.example.com"
config = """\
    location / {
        proxy_pass http://bar.example.com;
    }
"""
```

or, if possible, maybe named:

```toml
[http.servers.foo]
name = "foo.example.com"
config = """\
    location / {
        proxy_pass http://bar.example.com;
    }
"""
```