Knobs Addon: use CodeMirror (or other editor) for object knobs

[kohlmannj]

Implement CodeMirror or another (lighter-weight?) code editor for the object knob. This will allow the user to focus on the data they're inputting, rather than manually formatting a JSON object literal.

Related: #1186

[z4o4z]

@kohlmannj It is really good idea, I'll try to do it!)

[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. We do try to do some housekeeping every once in a while so inactive issues will get closed after 90 days. Thanks!

[stale]

Hey there, it's me again! I am going to help our maintainers close this issue so they can focus on development efforts 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!