docs: add Headlamp plugin guide

[mahmoudmagdy1-1]

Please check if the PR fulfills these requirements

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What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)
/kind documentation

What this PR does / why we need it:
This PR adds documentation for using the Volcano plugin for Headlamp from the Volcano website.
The update includes:

• An Ecosystem page introducing Headlamp on Volcano
• A User Guide page for installing the plugin from the Headlamp Plugin Catalog
• Supported Volcano resources shown in Headlamp
• Verification commands for Volcano Jobs, Queues, PodGroups, JobTemplates, and JobFlows
• Screenshots showing the Plugin Catalog, Volcano sidebar, Jobs view, Job details, and resource map
• References to Headlamp installation, plugin packaging docs, and the Volcano Headlamp plugin source
  This helps users discover and use the Headlamp plugin as a UI option for inspecting Volcano scheduling resources from an existing Kubernetes UI.

[volcano-sh-bot]

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[volcano-sh-bot]

Welcome @mahmoudmagdy1-1! It looks like this is your first PR to volcano-sh/website 🎉

[gemini-code-assist]

Code Review

This pull request introduces documentation for the Volcano Headlamp plugin, adding an introductory overview and a detailed user guide. The new content covers the plugin's features, installation steps, supported resources, and integration with the Headlamp resource map. Review feedback suggests improving the consistency and readability of the provided kubectl commands by using resource short names and shorthand flags.