[Storybook] Update utils to ensure properly merged story configs

[mgadewoll]

Summary

Our storybook utils to disable/hide/move component props in the controls table are currently generating and returning objects without context of any existing entries on the config it adds to (component or story level). While Storybook does merge configs (component and story level - story level overwrites component level) this can still result in the utils output potentially overwriting existing prop control definitions - e.g. when we call multiple utils on the same prop and in the same level (e.g. story level).

We want to update the utils to ensure they update the existing config instead of overwriting it.

💬 See this conversation for more information.

Acceptance criterea

• utils (hideStorybookControls, disableStorybookControls and moveStorybookControlsToCategory) don't overwrite other config entries but mutate the existing config while respecting existing entries
• props that are adjusted in the controls panel via utils are properly output (e.g. moved and disabled)

[github-actions[bot]]

👋 Hi there - this issue hasn't had any activity in 6 months. If the EUI team has not explicitly expressed that this is something on our roadmap, it's unlikely that we'll pick this issue up. We would sincerely appreciate a PR/community contribution if this is something that matters to you! If not, and there is no further activity on this issue for another 6 months (i.e. it's stale for over a year), the issue will be auto-closed.