Knobs Addon: support JavaScript objects (rather than JSON)

[kohlmannj]

Allow the object knob to support a JavaScript object rather than a JSON object. That way, the user doesn't have to manually type out a full, valid JSON object, which can be quite laborious.

[ndelangen]

Related: #1187

Want to make a PR @kohlmannj ?

[stale]

Hi everyone! Seems like there hasn't been much going on in this issue lately. If there are still questions, comments, or bugs, please feel free to continue the discussion. Unfortunately, we don't have time to get to every issue. We are always open to contributions so please send us a pull request if you would like to help. Inactive issues will be closed after 60 days. Thanks!

[stale]

Hey there, it's me again! I am going close this issue to help our maintainers focus on the current development roadmap instead. If the issue mentioned is still a concern, please open a new ticket and mention this old one. Cheers and thanks for using Storybook!