chore: update outdated links and remove Roadmap from nav menu

[FeynmanZhou]

Another two places are updated as follows based on the repo status changes.

• Remove Roadmap from the menu since the Roadmap repo is not in active maintenance now.
• Update the GitHub icon link from https://github.com/notaryproject/notaryproject to https://github.com/notaryproject/notation
• Update Notary Project link from https://github.com/notaryproject/notaryproject to https://github.com/notaryproject/.github

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[github-actions[bot]]

This PR is stale because it has been open 45 days with no activity. Remove stale label or comment or this will be closed in 30 days.

[yizha1]

@FeynmanZhou Please check the recent comments https://github.com/notaryproject/notaryproject.dev/pull/332#discussion_r1291801406, I got two votes.

[github-actions[bot]]

This PR is stale because it has been open 45 days with no activity. Remove stale label or comment or this will be closed in 30 days.

[github-actions[bot]]

This PR was closed because it has been stalled for 30 days with no activity.