[#493] cmd/node: Support duration type casting in config

Signed-off-by: Alex Vanin <alexey@nspcc.ru>

cmd/neofs-node/config/cast.go

@@ -1,6 +1,8 @@
 package config
 
 import (
+	"time"
+
 	"github.com/spf13/cast"
 )
 
@@ -47,3 +49,22 @@ func String(c *Config, name string) string {
 func StringSafe(c *Config, name string) string {
 	return cast.ToString(c.Value(name))
 }
+
+// Duration reads configuration value
+// from c by name and casts it to time.Duration.
+//
+// Panics if value can not be casted.
+func Duration(c *Config, name string) time.Duration {
+	x, err := cast.ToDurationE(c.Value(name))
+	panicOnErr(err)
+
+	return x
+}
+
+// DurationSafe reads configuration value
+// from c by name and casts it to time.Duration.
+//
+// Returns 0 if value can not be casted.
+func DurationSafe(c *Config, name string) time.Duration {
+	return cast.ToDuration(c.Value(name))
+}