Pull request 1892: next-imp-dnssvc

Squashed commit of the following:

commit 770a3f338ecb270fcff7792a4ffe3cf95492d2ae
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Tue Jun 27 20:10:39 2023 +0300

    dnssvc: fix test for darwin

commit 6564abcc0904784ff3787e1a046d665519a108b3
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Tue Jun 27 19:57:19 2023 +0300

    all: fix .gitignore, tests

commit 3ff1be0462b3adea81d98b1f65eeb685d2d72030
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Tue Jun 27 19:30:05 2023 +0300

    next: add conf example; imp dnssvc

internal/next/dnssvc/config.go

@@ -0,0 +1,35 @@
+package dnssvc
+
+import (
+	"net/netip"
+	"time"
+)
+
+// Config is the AdGuard Home DNS service configuration structure.
+//
+// TODO(a.garipov): Add timeout for incoming requests.
+type Config struct {
+	// Addresses are the addresses on which to serve plain DNS queries.
+	Addresses []netip.AddrPort
+
+	// BootstrapServers are the addresses of DNS servers used for bootstrapping
+	// the upstream DNS server addresses.
+	BootstrapServers []string
+
+	// UpstreamServers are the upstream DNS server addresses to use.
+	UpstreamServers []string
+
+	// DNS64Prefixes is a slice of NAT64 prefixes to be used for DNS64.  See
+	// also [Config.UseDNS64].
+	DNS64Prefixes []netip.Prefix
+
+	// UpstreamTimeout is the timeout for upstream requests.
+	UpstreamTimeout time.Duration
+
+	// BootstrapPreferIPv6, if true, instructs the bootstrapper to prefer IPv6
+	// addresses to IPv4 ones when bootstrapping.
+	BootstrapPreferIPv6 bool
+
+	// UseDNS64, if true, enables DNS64 protection for incoming requests.
+	UseDNS64 bool
+}