docs: add tiername usage documentation for NetworkTopologyAware

[vanshika2720]

What type of PR is this?

/kind documentation

What this PR does / why we need it:

This PR updates the NetworkTopologyAware documentation to include guidance for using highestTierName (tiername).

The feature was introduced in #4795, but the design document and user guide did not explain how to configure topology-aware scheduling using tier names. This PR adds documentation describing topology tiers, highestTierName behavior, configuration examples, and usage recommendations.

Which issue(s) this PR fixes:

Fixes #5483

Special notes for your reviewer:

• Updated the NetworkTopologyAware design document.
• Updated the user guide with configuration examples and usage guidance.
• Documentation only; no code changes.

Does this PR introduce a user-facing change?

Added documentation for the NetworkTopologyAware highestTierName (tiername) feature, including design details, configuration examples, and usage guidance.

[volcano-sh-bot]

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[gemini-code-assist]

Code Review

This pull request updates the documentation for Volcano's Network Topology Aware Scheduling to introduce topology tier selection using tier names (highestTierName) instead of only numerical levels. The review feedback highlights critical issues where the scheduler plugin does not currently parse highestTierName in its configuration, and the API check for hard topology mode fails to account for cases where only highestTierName is configured. Additionally, a correction is suggested to remove references to a non-existent tiername field in the documentation.

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[Copilot]

Pull request overview

This PR updates Volcano’s NetworkTopologyAware documentation to describe how to use highestTierName (tier name) for topology-aware scheduling boundaries, complementing the existing highestTierAllowed (numeric tier) guidance.

Changes:

• Documented highestTierName usage in the NetworkTopologyAware user guide, including examples and recommendations.
• Added a “Topology Tier Selection” section to the design document describing tier-name-based boundary selection.
• Minor markdown/formatting cleanups in existing YAML snippets.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 6 comments.

File	Description
docs/user-guide/how_to_use_network_topology_aware_scheduling.md	Adds highestTierName documentation, examples, and a new section about configuring tier selection (but currently describes unsupported scheduler plugin args).
docs/design/Network Topology Aware Scheduling.md	Adds design-level explanation of tier-name-based boundaries and default behavior (with some behavioral inaccuracies for soft mode).

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[vanshika2720]

/cc @hajnalmt
/cc @JesseStutler

[vanshika2720]

@hajnalmt Please review