docs(metrics): update the metrics documentation

[ttsuuubasa]

What type of PR is this?

/kind documentation
/area cluster-autoscaler

What this PR does / why we need it:

This PR expands the metrics documentation by adding the metrics that are not yet documented, and re-syncs proposals/metrics.md with metrics.go so the doc reflects the actual implementation.

cluster-autoscaler/proposals/metrics.md is one of the entry points users rely on to discover what metrics Cluster Autoscaler exposes, but a number of metrics defined in cluster-autoscaler/metrics/metrics.go have never been listed there. This makes it hard for operators to learn which metrics are available and what their labels are without reading the source code.

Newly documented metrics:

• Per-node-group metrics gated behind --emit-per-nodegroup-metrics
• failed_node_creations_total
• failed_gpu_scale_ups_total
• unneeded_nodes_count
• unremovable_nodes_count
• scale_down_in_cooldown
• overflowing_controllers_count
• created_node_groups_total
• deleted_node_groups_total
• node_taints_count
• inconsistent_instances_migs_count
• binpacking_heterogeneity
• max_node_skip_eval_duration_seconds
• node_removal_latency_seconds
• dra_node_template_resources_mismatch

Other changes:

• Reorder the "Cluster state" and "Cluster Autoscaler operations" tables to match the declaration order in metrics.go, so future drift is easier to spot.
• Fix labels on existing rows so they match what is actually emitted (e.g. add gpu_resource_name / dra_drivers to the scale-up/down rows, type to unschedulable_pods_count, eviction_result to evicted_pods_total).
• Mark scaled_up_gpu_nodes_total, scaled_down_gpu_nodes_total, and failed_gpu_scale_ups_total as deprecated since 1.36.0, in line with their DeprecatedVersion in code.

The doc is intentionally only re-synced; no metrics are added, removed or renamed in this PR.

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

Does this PR introduce a user-facing change?

NONE

Additional documentation e.g., KEPs (Kubernetes Enhancement Proposals), usage docs, etc.:

NONE

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[jackfrancis]

While we're here can we clean up nap_enabled, this metric no longer exists.

[jackfrancis]

Actually I think we can delete this entire section (starting from L159) as the node groups metrics were added above.