[Issue] Add note to clarify why you don't need to worry about data tiers in Serverless

[yetanothertw]

Stems from discussions and improvements identified in (#1531).

The data tiers page could benefit from an admonition similar to the one in the stack settings page, to help readers understand that this functionality is abstracted and automated in order to make cluster management easier.

@shainaraskas recommends:

• Adding something like: :::{admonition} Serverless manages data storage for you {{serverless-full}} scales with your workload and automates nodes, shards, and replicas for you. :::
• Connecting this note to the search AI lake concept (that provides similar tuning capability in a different way). For more info, see Benefits of serverless projects.
• Validating the final copy with product.