docs: Document Custom Links for Local UI

[lennessyy]

Describe the Change

This PR documents how to add custom links to local UI.

Changed Pages

💻 Add Preview URL for Page

Jira Tickets

🎫 PE-4193

Backports

Can this PR be backported?

• [ ] No. This is a release PR.

[netlify[bot]]

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[github-actions[bot]]

🤖 Netlify configured to enable preview build for branch: custom-link-localui . Subsequent commits will automatically trigger a Netlify build preview.

[vault-token-factory-spectrocloud[bot]]

Images automagically compressed by Calibre's image-actions ✨

Compression reduced images by 83.6%, saving 59.10 KB.

Filename	Before	After	Improvement	Visual comparison
static/assets/docs/images/clusters_edge_localui_custom-link-sidebar.webp	70.70 KB	11.60 KB	-83.6%	View diff

697 images did not require optimisation.

[vault-token-factory-spectrocloud[bot]]

Images automagically compressed by Calibre's image-actions ✨

Compression reduced images by 2.2%, saving 258 bytes.

Filename	Before	After	Improvement	Visual comparison
static/assets/docs/images/clusters_edge_localui_custom-link-sidebar.webp	11.60 KB	11.35 KB	-2.2%	View diff

697 images did not require optimisation.