Add Optional retrieveObjects to Include Content

[dansreis]

Description

We would like to add an optional feature to the retrieveObjects method in the react-canvas-annotator library. This feature should allow users to include the content of the objects when retrieving them. This enhancement will provide more flexibility and functionality for users who need detailed information about the objects on the canvas.

Motivation

Currently, the retrieveObjects method fetches objects from the canvas but does not include their content. Including the content of these objects will be beneficial for various use cases, such as saving and loading annotations, exporting data, or integrating with other systems.