Added undocumented CONSUL_NAMESPACE to website. (#8264)

website/pages/docs/commands/index.mdx

@@ -244,3 +244,14 @@ certificates](/docs/agent/encryption#rpc-encryption-with-tls), then the
 gRPC listener will require TLS and present the same certificate as the https
 listener. As with `CONSUL_HTTP_ADDR`, if TLS is enabled either the `https://`
 scheme should be used, or `CONSUL_HTTP_SSL` set.
+
+### `CONSUL_NAMESPACE`
+
+**Enterprise only**
+If you're using Consul Enterprise namespaces you can set this for the CLI to 
+explicitly use a single namespace.  This is common across all Hashicorp 
+products that support Enterprise namespaces.
+
+```
+CONSUL_NAMESPACE=default
+```