fix: Updates navigation placement for redesign.

[edonehoo]

Replaced #814

As part of patternfly/patternfly-org#4753

Follow-up work would include

1. Updating the about/overview page with more details on usage
2. Potentially replacing current conceptual nav groups with flyout menus: pf nav doesn't support a third tier which is required to nest this under extensions. Flyout is a possible alternative, but not sure that the framework supports flyout yet. The plan is to merge this & also parent issue prs first and then continue fixing these gaps
3. Replacing or fixing the existing gallery functionality to align with this decision

[patternfly-build]

Preview: https://react-component-groups-pr-component-groups-838.surge.sh

A11y report: https://react-component-groups-pr-component-groups-838-a11y.surge.sh

[github-actions]

🎉 This PR is included in version 6.4.0-prerelease.5 🎉

The release is available on:

• GitHub release
• npm package (@prerelease dist-tag)

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