Add note that durable writes are not supported for number of replicas > 2

Transactions documentation mentions issues with durable writes on single-node cluster, but I recently found that the server does not support durable writes when the bucket is configured with 3 replicas.

So maybe it makese sense to update documentation for user awareness.
https://docs.couchbase.com/server/current/learn/data/transactions.html#deployment-considerations

The server change is documented at MB-34453. On UI this is visible when one tries to change default durability level for the bucket when 3 replicas configured. But with default durability level set to NONE, it still allows using 3 replicas and the SDK will always return DurabilityImpossible error for all mutations with any other durability level except NONE.

There is no customer ticket associated with this request, as using 3 replicas in production must be rare case.