Clarify number of deployed services in Get Started (#67574)

Closes #67534

Fix the preamble to the list of services to include the correct count.
Make it clear that the list of three services refers to the services
deployed for the getting started guide. Use the terms control plane vs.
Teleport Agent service to indicate which aspects of the starter cluster
belong to a Teleport cluster in general.

docs/pages/get-started/deploy-community.mdx

@@ -19,7 +19,7 @@ You'll spin up a single-instance Teleport cluster on a Linux server, ideal for s
 
 ## How it works
 
-The Teleport cluster consists of two services:
+The Teleport cluster we set up in this guide consists of three services:
 
 - **Teleport Auth Service:** The certificate authority for your cluster. It
   issues certificates and conducts authentication challenges. The Auth Service
@@ -31,6 +31,11 @@ The Teleport cluster consists of two services:
   controls, records sessions, and logs activity as Teleport audit events,
   enabling you to protect a Linux server with Teleport.
 
+The Teleport Auth Service and Proxy Service are considered the **control
+plane**. In Teleport Cloud, they run on Teleport-managed infrastructure. The
+Teleport SSH Service is an example of a **Teleport Agent** service, which
+proxies connections to and from a resource in your infrastructure.
+
 ![Architecture of the setup you will complete in this
 guide](../../img/linux-server-diagram.png)