[docs] add batching in limitations of key-shared mode (#9153)
[docs] add batching in limitations of key-shared mode (#9153)

### Motivation

Using KeyShared with batching can lead to vicious bugs as batching remove the guarantee of having a unique consumer handling a given key. I've spent some time debugging this and think it worth stating that in the key-shared limitation

### Modifications

Just added Batching as a limitation of Key-Shared mode. 

### Verifying this change

This change is a trivial rework / code cleanup without any test coverage.

yes

This change is already covered by existing tests, such as *(please describe tests)*.

yes


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