Add new site config sub-system intended to replace region (#13672)

- New sub-system has "region" and "name" fields.

- `region` subsystem is marked as deprecated, however still works, unless the
new region parameter under `site` is set - in this case, the region subsystem is
ignored. `region` subsystem is hidden from top-level help (i.e. from `mc admin
config set myminio`), but appears when specifically requested (i.e. with `mc
admin config set myminio region`).

- MINIO_REGION, MINIO_REGION_NAME are supported as legacy environment variables for server region.

- Adds MINIO_SITE_REGION as the current environment variable to configure the
server region and MINIO_SITE_NAME for the site name.

cmd/globals.go

@@ -29,6 +29,7 @@ import (
 	"github.com/minio/console/restapi"
 	"github.com/minio/minio-go/v7/pkg/set"
 	"github.com/minio/minio/internal/bucket/bandwidth"
+	"github.com/minio/minio/internal/config"
 	"github.com/minio/minio/internal/handlers"
 	"github.com/minio/minio/internal/kms"
 	"github.com/rs/dnscache"
@@ -148,8 +149,9 @@ var (
 	// This flag is set to 'true' when MINIO_UPDATE env is set to 'off'. Default is false.
 	globalInplaceUpdateDisabled = false
 
-	// This flag is set to 'us-east-1' by default
-	globalServerRegion = globalMinioDefaultRegion
+	globalSite = config.Site{
+		Region: globalMinioDefaultRegion,
+	}
 
 	// MinIO local server address (in `host:port` format)
 	globalMinioAddr = ""