fix(website): fix docs sidebar expand/collapse navigation

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Summary

• Use strings.HasPrefix to keep sections expanded when on any child page (the previous eq check only matched the section index, not child pages)
• Add @click="open = true" to section title links so clicking the title expands the group in addition to navigating, without requiring the chevron

Vector configuration

How did you test this PR?

Change Type

• Bug fix
• New feature
• Dependencies
• Non-functional (chore, refactoring, docs)
• Performance

Is this a breaking change?

• Yes
• No

Does this PR include user facing changes?

• Yes. Please add a changelog fragment based on our guidelines.
• No. A maintainer will apply the no-changelog label to this PR.

References

Notes

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All contributors have signed the CLA ✍️ ✅
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I have read the CLA Document and I hereby sign the CLA

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[pront]

This is a great enhancement, thanks