Add example query with an Entry in the SELECT clause

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Selecting the complete entry in a SELECT clause is a common requirement when users want to avoid cartesian product of sibling elements within the entry. For example, an OBSERVATION containing a CLUSTER with N ELEMENTs would create N rows in the result set, so selecting the parent OBSERVATION directly is a common approach.

Provide an example that shows how we can build a query that selects the whole ENTRY