docs(TreeView): Update TreeView example

[silvalaura]

Issue: none

What I did

Adding a description for checkChildren and checkParents prop to the docs site, and updating the example in storybook to confirm that the expected items are selected.

Screenshots:

Checklist

• [X] changeset has been added
• [X] Pull request description is descriptive
• [X] I have made corresponding changes to the documentation
• [X] New and existing unit tests pass locally with my changes
• [-] I have added tests that prove my fix is effective or that my feature works

How to test

Ensure that the docs site has the appropriate amount of information for adopters to understand these new props.

[changeset-bot[bot]]

🦋 Changeset detected

Latest commit: 36155309afa1ac73c29ee3a302b7cd0dfd874ed9

The changes in this PR will be included in the next version bump.

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Click here if you're a maintainer who wants to add another changeset to this PR

[github-actions[bot]]

🚀 Deployed on https://docs-preview-1416--upbeat-sinoussi-f675aa.netlify.app

[github-actions[bot]]

🚀 Deployed on https://storybook-preview-1416--upbeat-sinoussi-f675aa.netlify.app

[orion-cengage]

Looks great from my side.