Add SRV Record Support

[edoardottt]

Please describe your feature request:

Add support for querying SRV records too (as described in RFC2782).

Describe the use case of this feature:

package main

import (
    "log"

    "github.com/projectdiscovery/retryabledns"
    "github.com/miekg/dns"
)

func main() {
    // it requires a list of resolvers
    resolvers := []string{"8.8.8.8:53", "8.8.4.4:53"}
    retries := 2
    hostname := "_xmpp-client._tcp.jabber.org"
    dnsClient := retryabledns.New(resolvers, retries)

    dnsResponses, err := dnsClient.Query(hostname, dns.TypeSRV)
    if err != nil {
        log.Fatal(err)
    }

    log.Println(dnsResponses)
}