feat(root): added new code examples to top nav code page

[GCHQ-Developer-741]

Summary of the changes

Added new code examples to top nav to show off:

• Conditionally rendering tabs #910
• Using GatsbyLinks https://github.com/mi6/ic-ui-kit/issues/1244

Accompanies an ic-ui-kit PR aiming to bring ic-top-navigation in line with the PR checklist (https://github.com/mi6/ic-ui-kit/pull/1872)

Checklist

• [x] I have manually accessibility tested any changes, if relevant.
• [x] I have raised this pull request against the develop branch

[github-actions[bot]]

View your branch deployment here: https://mi6.github.io/ic-design-system-githubpages/branches/910-new-top-nav-code-examples