Documentation: add description of copy-keyword-arguments-on-return behavior

[by321]

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Is your feature request related to a problem? Please describe.

As output, most (if not all) components can take a returned component of the same type, and in this case, the gradio framework will copy the values of keyword arguments that were used to create the returned component to the existing component. This unexpected behavior is not clearly documented.

Describe the solution you'd like

Describe this behavior on the Components page, or add a separate page for Component (the base class all component classes are derived from) and describe it there, along with other things worth mentioning.

Then in the individual component class pages, add reference to this behavior and a link to the Components or Component page. For example, the Image documentation should say:

As output component: Expects a numpy.array, PIL.Image, or str or pathlib.Path filepath to an image which is displayed. Alternatively, a gradio Image component, and in this case the values of keyword arguments used to create the returned component will be copied to the output component. See Components or Component page (with link).