docs: update outdated guide to make code open by default

[abiriadev]

What I did

For storybook 7 or higher, the code below does not work.

export const parameters = {
  docs: {
    source: {
      state: 'open',
    },
  },
};

It should be fixed like below:

export const parameters = {
  docs: {
    canvas: {
      sourceState: 'shown'
    }
  }
};

However, this document seems not changed so far. So I updated it.

References:

• https://storybook.js.org/docs/api/doc-block-canvas#sourcestate
• docs: Show Code Open by default  #10430

Checklist for Contributors

Testing

The changes in this PR are covered in the following automated tests:

• stories
• unit tests
• integration tests
• end-to-end tests

Manual testing

This is a document change, no testing is required.

Documentation

• Add or update documentation reflecting your changes
• If you are deprecating/removing a feature, make sure to update
  MIGRATION.MD

Checklist for Maintainers

• When this PR is ready for testing, make sure to add ci:normal, ci:merged or ci:daily GH label to it to run a specific set of sandboxes. The particular set of sandboxes can be found in code/lib/cli/src/sandbox-templates.ts

• Make sure this PR contains one of the labels below:

  Available labels

  • bug: Internal changes that fixes incorrect behavior.
  • maintenance: User-facing maintenance tasks.
  • dependencies: Upgrading (sometimes downgrading) dependencies.
  • build: Internal-facing build tooling & test updates. Will not show up in release changelog.
  • cleanup: Minor cleanup style change. Will not show up in release changelog.
  • documentation: Documentation only changes. Will not show up in release changelog.
  • feature request: Introducing a new feature.
  • BREAKING CHANGE: Changes that break compatibility in some way with current major version.
  • other: Changes that don't fit in the above categories.