migrate all bucket metadata into a single file (#9586)

this is a major overhaul by migrating off all
bucket metadata related configs into a single
object '.metadata.bin' this allows us for faster
bootups across 1000's of buckets and as well
as keeps the code simple enough for future
work and additions.

Additionally also fixes #9396, #9394

cmd/admin-handlers.go

@@ -21,6 +21,7 @@ import (
 	"crypto/subtle"
 	"crypto/tls"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"io"
 	"net/http"
@@ -897,7 +898,7 @@ func toAdminAPIErr(ctx context.Context, err error) APIError {
 			HTTPStatusCode: e.StatusCode,
 		}
 	default:
-		if err == errConfigNotFound {
+		if errors.Is(err, errConfigNotFound) {
 			apiErr = APIError{
 				Code:           "XMinioConfigError",
 				Description:    err.Error(),