fast release is now self-serve for user

"Fast Release" is only available for the production tier and is a self-serve process accessible through the UI. Rewording this as the previous message may cause ambiguity for customers using the development tier, where the UI does not support the Fast Release option.

Author: allegrinisante

docs/en/cloud/manage/upgrades.md

@@ -23,7 +23,7 @@ You will not be charged for the time that the service is under maintenance. _Mai
 
 ## Release channels (upgrade schedule)
 
-You are able to specify the upgrade schedule for your ClickHouse Cloud service by subscribing to a specific release channel. Besides the regular upgrade schedule, we offer a **Fast release** channel if you would like your services to receive updates ahead of the regular release schedule. Subscribing to the **Fast release** channel for early upgrades is recommended only for non-production environments and can be requested by logging a support ticket.
+You are able to specify the upgrade schedule for your ClickHouse Cloud service by subscribing to a specific release channel. Besides the regular upgrade schedule, we offer a **Fast release** channel if you would like your services to receive updates ahead of the regular release schedule. Subscribing to the **Fast release** channel for early upgrades is recommended only for non-production environments.
 
 ### Fast release channel (early upgrades)