Pull request: 1992 configurable timeouts

Merge in DNS/adguard-home from 1992-conf-timeouts to master

Updates #1992.

Squashed commit of the following:

commit 1050c54fb407bec0617728690763b0392b3440b0
Merge: 05f71c3e 59544160
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Fri Aug 27 20:04:25 2021 +0300

    Merge branch 'master' into 1992-conf-timeouts

commit 05f71c3e5397909d943e69d49a247bf4f67619b0
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Fri Aug 27 20:03:06 2021 +0300

    home: use const

commit d0861792b42e6d066aa3ffdb3937e29477235ee0
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Fri Aug 27 19:16:26 2021 +0300

    home: fix default timeout

commit ba26fcdcf66366350c89d5a82c4da91ade45838f
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Fri Aug 27 16:50:33 2021 +0300

    all: mk ping timeout configurable

internal/aghtime/duration.go

@@ -0,0 +1,68 @@
+// Package aghtime defines some types for convenient work with time values.
+package aghtime
+
+import (
+	"time"
+
+	"github.com/AdguardTeam/golibs/errors"
+)
+
+// Duration is a wrapper for time.Duration providing functionality for encoding.
+type Duration struct {
+	// time.Duration is embedded here to avoid implementing all the methods.
+	time.Duration
+}
+
+// String implements the fmt.Stringer interface for Duration.  It wraps
+// time.Duration.String method and additionally cuts off non-leading zero values
+// of minutes and seconds.  Some values which are differ between the
+// implementations:
+//
+//   Duration:   "1m", time.Duration:   "1m0s"
+//   Duration:   "1h", time.Duration: "1h0m0s"
+//   Duration: "1h1m", time.Duration: "1h1m0s"
+//
+func (d Duration) String() (str string) {
+	str = d.Duration.String()
+
+	const (
+		tailMin    = len(`0s`)
+		tailMinSec = len(`0m0s`)
+
+		secsInHour = time.Hour / time.Second
+		minsInHour = time.Hour / time.Minute
+	)
+
+	switch rounded := d.Duration / time.Second; {
+	case
+		rounded == 0,
+		rounded*time.Second != d.Duration,
+		rounded%60 != 0:
+		// Return the uncutted value if it's either equal to zero or has
+		// fractions of a second or even whole seconds in it.
+		return str
+
+	case (rounded%secsInHour)/minsInHour != 0:
+		return str[:len(str)-tailMin]
+
+	default:
+		return str[:len(str)-tailMinSec]
+	}
+}
+
+// MarshalText implements the encoding.TextMarshaler interface for Duration.
+func (d Duration) MarshalText() (text []byte, err error) {
+	return []byte(d.String()), nil
+}
+
+// UnmarshalText implements the encoding.TextUnmarshaler interface for
+// *Duration.
+//
+// TODO(e.burkov): Make it able to parse larger units like days.
+func (d *Duration) UnmarshalText(b []byte) (err error) {
+	defer func() { err = errors.Annotate(err, "unmarshalling duration: %w") }()
+
+	d.Duration, err = time.ParseDuration(string(b))
+
+	return err
+}