flatten out audit tags, do not send as free-form (#20256)

move away from map[string]interface{} to map[string]string
to simplify the audit, and also provide concise information.

avoids large allocations under load(), reduces the amount
of audit information generated, as the current implementation
was a bit free-form. instead all datastructures must be
flattened.

cmd/fmt-gen.go

@@ -15,8 +15,6 @@
 // You should have received a copy of the GNU Affero General Public License
 // along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
-//go:build fmtgen
-
 package cmd
 
 import (
@@ -51,6 +49,7 @@ var fmtGenCmd = cli.Command{
 	Usage:  "Generate format.json files for an erasure server pool",
 	Flags:  append(fmtGenFlags, GlobalFlags...),
 	Action: fmtGenMain,
+	Hidden: true,
 	CustomHelpTemplate: `NAME:
   {{.HelpName}} - {{.Usage}}