Remove api.HostStats

[peterjan]

Closes #940

[Copilot]

Pull request overview

Removes the legacy ?response=prometheus query parameter behavior from the admin JSON endpoints now that Prometheus metrics are consolidated under /prometheus/metrics, and simplifies host-stats Prometheus marshalling to avoid wrapper types.

Changes:

• Replace writeResponse(..., resp) usage with direct jc.Encode(...) across admin endpoints (removing per-endpoint Prometheus formatting).
• Remove the HostStats wrapper type and make HostStatsResponse directly a []hosts.HostStats, updating Prometheus marshalling accordingly.
• Add a knope changeset documenting the user-facing change.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
api/admin/types.go	Removes the HostStats wrapper and updates HostStatsResponse to use hosts.HostStats directly.
api/admin/prometheus.go	Refactors host stats Prometheus metric generation to work directly with hosts.HostStats.
api/admin/admin.go	Removes writeResponse and switches handlers to always return JSON via jc.Encode; updates /prometheus/metrics to wrap host stats correctly.
.changeset/remove_prometheus_response_format_from_stats_endpoints.md	Adds release-note entry for the removed query parameter behavior.

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[ChrisSchinnerl]

Looking good but before we merge this we should update the deploy repo to pull in the stats from the new route.

[n8mgr]

Why are you removing the response format from the other endpoints?