Add any plugin (#2801)

* Add any plugin

This adds the any plugin, a plain copy of coredns/any documented here
https://coredns.io/explugins/any/ as an external plugin.

Fixes: #2785

Signed-off-by: Miek Gieben <miek@miek.nl>

* Stickler bot nit

Signed-off-by: Miek Gieben <miek@miek.nl>

plugin/any/any_test.go

@@ -0,0 +1,28 @@
+package any
+
+import (
+	"context"
+	"testing"
+
+	"github.com/coredns/coredns/plugin/pkg/dnstest"
+	"github.com/coredns/coredns/plugin/test"
+
+	"github.com/miekg/dns"
+)
+
+func TestAny(t *testing.T) {
+	req := new(dns.Msg)
+	req.SetQuestion("example.org.", dns.TypeANY)
+	a := &Any{}
+
+	rec := dnstest.NewRecorder(&test.ResponseWriter{})
+	_, err := a.ServeDNS(context.TODO(), rec, req)
+
+	if err != nil {
+		t.Errorf("Expected no error, but got %q", err)
+	}
+
+	if rec.Msg.Answer[0].(*dns.HINFO).Cpu != "ANY obsoleted" {
+		t.Errorf("Expected HINFO, but got %q", rec.Msg.Answer[0].(*dns.HINFO).Cpu)
+	}
+}