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/common-main.go

@@ -187,7 +187,7 @@ func minioConfigToConsoleFeatures() {
 			os.Setenv("CONSOLE_IDP_CALLBACK", getConsoleEndpoints()[0]+"/oauth_callback")
 		}
 	}
-	os.Setenv("CONSOLE_MINIO_REGION", globalServerRegion)
+	os.Setenv("CONSOLE_MINIO_REGION", globalSite.Region)
 	os.Setenv("CONSOLE_CERT_PASSWD", env.Get("MINIO_CERT_PASSWD", ""))
 	if globalSubnetConfig.License != "" {
 		os.Setenv("CONSOLE_SUBNET_LICENSE", globalSubnetConfig.License)