Link to the status page for cloud

For someone unfamiliar with the status page as being the source of truth
for scheduled upgrades, the "Teleport Cloud" section on the "Upcoming Releases" document can give a false impression that the next update will be further in the future than it really is.

Adding a link to the status page will help discoverability of the next
upcoming change to Cloud, even if it isn't a "key deliverable" for that
quarter.

docs/pages/upcoming-releases.mdx

@@ -113,6 +113,10 @@ The key deliverables for Teleport Cloud in the next quarter:
 | June 5th, 2023   | Teleport 13.1 begins to roll out for Cloud customers |
 | June 5th, 2023   | Advanced Audit Log rollout begins                    |
 
+Subscribe to status updates at
+[status.teleport.sh](https://status.teleport.sh/) for regular Cloud upgrade
+notifications.
+
 ## Production readiness
 
 Teleport follows [semantic versioning](https://semver.org) for pre-releases and