func New(config json.RawMessage) (Checker, error) {
	var checker Checker
	err := json.Unmarshal(config, &checker)
	return checker, err
}
New creates a new Checker instance based on json config
package dns
import (
	"encoding/json"
	"fmt"
	"net"
	"time"
	"github.com/miekg/dns"
	"github.com/sourcegraph/checkup/types"
)
const Type = "dns"
type Checker struct {
	Name string `json:"endpoint_name"`
	URL string `json:"endpoint_url"`
	Host string `json:"hostname_fqdn,omitempty"`
	Timeout time.Duration `json:"timeout,omitempty"`
	ThresholdRTT time.Duration `json:"threshold_rtt,omitempty"`
	Attempts int `json:"attempts,omitempty"`
}