Pull request: 2280 dns timeout

Updates #2280.

Squashed commit of the following:

commit d8c6aacb664361a13dde8522de2470dd137bed00
Merge: 84df492b 12f1e4ed
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Tue Jun 15 17:21:41 2021 +0300

    Merge branch 'master' into 2280-dns-timeout

commit 84df492b0134e88e031f586333437f503b90b7ae
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Tue Jun 15 16:49:41 2021 +0300

    home: fix docs & naming

commit af44a86a60ea815ca7100edc34db8acbdcc2cccf
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Tue Jun 15 15:55:12 2021 +0300

    all: imp docs & tests

commit 6ed6599fa0024cc7d14dc7c75ddda62e5179fe00
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Tue Jun 15 15:26:22 2021 +0300

    home: imp duration tests

commit 8fe7cb099dccfce3f9329d7207ef48f488f07e83
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Tue Jun 15 15:04:16 2021 +0300

    all: imp code, docs & tests

commit a989e8a5a6acede0063141cdbfc103b150b33d97
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Sat Jun 12 19:02:23 2021 +0300

    WIP

commit b0362e22040a1d38f81dcc775c5ef6f7d1e94eee
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Sat Jun 12 18:58:09 2021 +0300

    all: imp docs & tests

commit 64b00fd0854f3ddcb0189f3c93f3ffa2a31a98be
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Sat Jun 12 03:44:29 2021 +0300

    home: introduce marshalable duration

commit bfb1a5706c37fcd27bccce4a5aec37dca3cf238b
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Sat Jun 12 01:56:10 2021 +0300

    all: add upstream timeout setting

internal/home/duration.go

@@ -0,0 +1,28 @@
+package home
+
+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
+}
+
+// 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.
+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
+}