Enable dualstack in every net.Dialer, fixes #9364

Default transport enables it:

* https://github.com/golang/go/blob/d2826d3e06/src/net/http/transport.go#L42-L46

```
    DialContext: (&net.Dialer{
	Timeout:   30 * time.Second,
	KeepAlive: 30 * time.Second,
	DualStack: true,
    }).DialContext,
```

See also: https://github.com/golang/go/issues/15324

closes #9355

Remove duplicate "to", and "others" is plural not possessive.

(prometheus) instant query support

these scenarios makes it easier debug panels based
on the same numbers without sharing datasource

ref #9332

introduce smtp config option for EHLO identity