feat: StructuredOutput returns list of Data objects when multiple=True

[elephantum]

Description

This PR proposes a change in Structured Output behavior when Generate Multiple is set to true.

Currently when Generate Multiple is used component produces a single Data entry with single key objects which contains a string representation of a json list of records. This is a bit counterintuitive because Langflow supports input and output of lists of Data objects.

Solution

We propose to change semantics of Structured Output to return a list Data objects when Generate Multiple is enabled