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.

internal/config/help.go

@@ -49,13 +49,34 @@ func (hkvs HelpKVS) Lookup(key string) (HelpKV, bool) {
 // DefaultComment used across all sub-systems.
 const DefaultComment = "optionally add a comment to this setting"
 
-// Region and Worm help is documented in default config
+// Region help is documented in default config
 var (
+	SiteHelp = HelpKVS{
+		HelpKV{
+			Key:         NameKey,
+			Type:        "string",
+			Description: `name for the site e.g. "cal-rack0"`,
+			Optional:    true,
+		},
+		HelpKV{
+			Key:         RegionKey,
+			Type:        "string",
+			Description: `name of the location of the server e.g. "us-west-1"`,
+			Optional:    true,
+		},
+		HelpKV{
+			Key:         Comment,
+			Type:        "sentence",
+			Description: DefaultComment,
+			Optional:    true,
+		},
+	}
+
 	RegionHelp = HelpKVS{
 		HelpKV{
 			Key:         RegionName,
 			Type:        "string",
-			Description: `name of the location of the server e.g. "us-west-rack2"`,
+			Description: `[DEPRECATED] name of the location of the server e.g. "us-west-rack2"`,
 			Optional:    true,
 		},
 		HelpKV{