Add diagram

Author: anthonychu

articles/container-apps/media/sessions/sessions-overview.png

@@ -71,6 +71,8 @@ To send an HTTP request to a session, you must provide a session identifier in t
 * If a session with the identifier already exists, the request is sent to the existing session.
 * If a session with the identifier doesn't exist, a new session is automatically allocated before the request is sent to it.
 
+:::image type="content" source="media/sessions-overview.png" alt-text="Session pool and sessions usage":::
+
 #### Identifier format
 
 The session identifier is a free-form string, meaning you can define it in any way that suits your application's needs.