Add possibility to alter data before *.stories.json generation

Problem/Motivation

Sometimes, it would be great to have the possibility to change or add some data inside generated *.stories.json.
For example some data for Storybook automatic docs integration, or code examples for stories.

Steps to reproduce

1. Add some stories using *.stories.twig and try to add some additional parameters to the "with" section.
2. Run "drush storybook:generate-all-stories"
3. Ensure that there is no possibility of passing some additional data (all of that skipped)

Proposed resolution

Add some alteration possibilities to data provided by "$this->storyRenderer
->generateStoriesJsonFile($template_path, $url)" method inside "generateStoriesForTemplate" command