[Docs] Atomicity Limitations of xCluster Need to be Clearer

[mrajcevic01]

Description

I have created this issue in response to a conversation with a user that was confused by the documentation below.

Currently in our xCluster documentation we have a section called Limitations that calls out the current limitations of the feature.

In the Transactional semantics subsection we see:

"Transactions from the source are not applied atomically on the target. That is, some changes in a transaction may be visible before others."

However further down in the Atomicity of Transactions subsection under Transactional guarantees we see:

"This implies one can never read a partial result of a transaction on the sink cluster."

This is confusing for users as Atomicity is only guaranteed on the target side if a transaction impacts a single shard/tablet. If the transaction touches multiple shards or multiple tables, then currently atomicity across shards/tables is not guaranteed on the target side. We are addressing this as part of Issue #10976 and it will be part of our upcoming release which should be available in Nov.

[lizayugabyte]

@mrajcevic01 I removed the "Atomicity of Transactions" section. And issue 10976 is already mentioned in Transactional semantics