test(router): prevent observability contract drift

[kube-gopher]

What type of PR is this?
/kind enhancement

What this PR does / why we need it:

• render the Helm chart with non-default ports and both HTTP and TLS settings, then verify router container/Service port wiring and health/readiness probes;
• assert the exact JSON field set emitted by a fully populated access-log entry and the required fields retained for a minimal entry;
• parse the example Grafana dashboard as JSON and verify every referenced kthena_router_* PromQL metric name maps to a registered collector, including histogram _bucket, _count, and _sum series;
• verify router metric names listed in the canonical observability guide map to registered router collectors.

Which issue(s) this PR fixes:
Fixes #1510

Bug evidence (required for bug-related PRs):

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

[volcano-sh-bot]

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[kube-gopher]

Previously, there were instances of obsolescence or disconnects among related documents, metrics, Helm charts, and so on, so I added an automatic detection and discovery mechanism; for example : #1499

[kube-gopher]

/cc @YaoZengzeng @acsoto

[kube-gopher]

From a long-term perspective, I think it's worth it because there's no need for manual review

[LiZhenCheng9527]

Nice.