Add --bind-conf flag for BIND domains.conf generation

Generate a BIND-format domains.conf file alongside catalog zones.
New input properties: file= (zone data path) and dnssec (bare flag).
When --bind-conf is set, every zone must have file= or it errors.

Renames ZoneEntry.File to ZonesFile (input path for error messages)
and adds ZoneFile (BIND file path) and DNSSEC (bool) fields.

catalog.go

@@ -85,7 +85,7 @@ func generateCatalogZone(catName string, cfg *Config, members []ZoneEntry, seria
 		h := hashZoneName(entry.Zone)
 		if existing, ok := hashToZone[h]; ok && existing != entry.Zone {
 			return "", fmt.Errorf("%s:%d: hash collision between %s and %s in catalog %q",
-				entry.File, entry.Line, existing, entry.Zone, catName)
+				entry.ZonesFile, entry.Line, existing, entry.Zone, catName)
 		}
 		hashToZone[h] = entry.Zone
 		zoneHash[entry.Zone] = h