cherry-pick: all: imp updater

Merge in DNS/adguard-home from imp-updater to master

Squashed commit of the following:

commit 6ed487359e56a35b36f13dcbf2efbf2a7a2d8734
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Thu Jun 9 16:29:35 2022 +0300

    all: imp logs, err handling

commit e930044cb619a43e5a44c230dadbe2228e9a93f5
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Thu Jun 9 15:53:35 2022 +0300

    all: imp updater

internal/aghalg/nullbool.go

@@ -0,0 +1,59 @@
+package aghalg
+
+import (
+	"bytes"
+	"encoding/json"
+	"fmt"
+)
+
+// NullBool is a nullable boolean.  Use these in JSON requests and responses
+// instead of pointers to bool.
+type NullBool uint8
+
+// NullBool values
+const (
+	NBNull NullBool = iota
+	NBTrue
+	NBFalse
+)
+
+// String implements the fmt.Stringer interface for NullBool.
+func (nb NullBool) String() (s string) {
+	switch nb {
+	case NBNull:
+		return "null"
+	case NBTrue:
+		return "true"
+	case NBFalse:
+		return "false"
+	}
+
+	return fmt.Sprintf("!invalid NullBool %d", uint8(nb))
+}
+
+// BoolToNullBool converts a bool into a NullBool.
+func BoolToNullBool(cond bool) (nb NullBool) {
+	if cond {
+		return NBTrue
+	}
+
+	return NBFalse
+}
+
+// type check
+var _ json.Unmarshaler = (*NullBool)(nil)
+
+// UnmarshalJSON implements the json.Unmarshaler interface for *NullBool.
+func (nb *NullBool) UnmarshalJSON(b []byte) (err error) {
+	if len(b) == 0 || bytes.Equal(b, []byte("null")) {
+		*nb = NBNull
+	} else if bytes.Equal(b, []byte("true")) {
+		*nb = NBTrue
+	} else if bytes.Equal(b, []byte("false")) {
+		*nb = NBFalse
+	} else {
+		return fmt.Errorf("unmarshalling json data into aghalg.NullBool: bad value %q", b)
+	}
+
+	return nil
+}