[#578] gendoc: Add date to man pages

```
HISTORY
       8-Aug-2023 Auto generated by spf13/cobra
```

Signed-off-by: Evgenii Stratonikov <e.stratonikov@yadro.com>

pkg/util/gendoc/gendoc.go

@@ -7,6 +7,7 @@ import (
 	"path/filepath"
 	"strings"
 	"text/template"
+	"time"
 
 	"github.com/spf13/cobra"
 	"github.com/spf13/cobra/doc"
@@ -31,9 +32,11 @@ type Options struct {
 
 func (o *Options) fillDefaults() {
 	if o.ManHeader == nil {
+		now := time.Now()
 		o.ManHeader = &doc.GenManHeader{
 			Section: "1",
 			Source:  "FrostFS",
+			Date:    &now,
 		}
 	}
 }