Update controller.mdx - public_cluster_addr (#5151)

* Update controller.mdx - public_cluster_addr

Updating public_cluster_addr to indicate that it is used if a load balancer is used for controllers. Also added a note about not including https:// and http:// in the address

* docs: Minor rewrite

* docs: Minor rewrite

---------

Co-authored-by: Dan Heath <76443935+Dan-Heath@users.noreply.github.com>

website/content/docs/configuration/controller.mdx

@@ -77,11 +77,12 @@ description will be read.
   optionally port) at which the controller can be reached _by workers_. This will
   be used by workers after initial connection to controllers via the worker's
   `initial_upstreams` block. This defaults to the address of the listener marked for
-  `cluster` purpose. This is especially useful for cloud environments that do not
+  `cluster` purpose. It is used if there is a load balancer in front of multiple Boundary controllers. This is also especially useful for cloud environments that do not
   bind a publicly accessible IP to a NIC on the host directly, such as an Amazon
   EIP. This value can be a direct address string, can refer to a file on disk (file://)
   from which an address will be read; an env var (env://) from which the
-  address will be read; or a [go-sockaddr template](https://godoc.org/github.com/hashicorp/go-sockaddr/template).
+  address will be read; or a [go-sockaddr template](https://godoc.org/github.com/hashicorp/go-sockaddr/template). 
+  Note that the address should not include the protocol prefixes like `http://` or `https://`.
 
 - `auth_token_time_to_live` - Maximum time to live (TTL) for all auth tokens globally (pertains
   to all tokens from all auth methods). Valid time units are anything specified by Golang's