Notebook Diff: options to filter outputs and metadata

[rebornix]

Though it's notebook content provider's decision to persistent cell metadata and outputs, users might not want to see them in the diff editor. To support this, we can

• introduce settings to control the behavior of whether outputs/metadata should be rendered in Notebook Diff editor
• allow toggle visibility of outputs and metadata in a diff editor, similar to "Render Whitespace Differences" or "Inline/Side-by-side view" action