[BUG]: imperfect type definitions around graph export features

Description

I found the following imperfect definitions in type definitions Plotly introduced recently (v4.0.0?), around toImage(), downloadImage() and config.toImageButtonOptions. This will hinder using these functions/option for TypeScript users (like me).

• Lack of full-json export format. A graph can be exported as JSON probably since v1.53.0 (see CHANGELOG.md or #4593) but this feature was not documented until very recently (plotly/graphing-library-docs#471).
• Lack of imageDataOnly option. This option is also very recently documented here.
• Some properties being set as required. The properties of the second parameter in toImage() and downloadImage() should be all optional. Currently some are required.

Can I send a PR for these? The PR won't include changes on executable code in JS; it will only modify *.d.ts files and maybe docstring parts in JS files.

Individua le definizioni *.d.ts di toImage(), downloadImage() e config.toImageButtonOptions, quindi confrontale con le funzionalità di esportazione documentate e con CHANGELOG.md. Verifica che full-json e imageDataOnly siano rappresentati e che le proprietà del secondo parametro siano opzionali; le modifiche alle definizioni dei tipi dovrebbero essere coperte dai controlli esistenti del repository.