observability(runway): restructure artifact-registry remote dashboard into format rows

Restructures dashboards/artifact-registry-gke/remote.dashboard.jsonnet into the layout the hosted dashboard uses: a top cross-format health row built only from format-comparable or format-neutral metrics, then one collapsed row per format for that format's own vocabulary. A new format adds one collapsed row and touches nothing else. All existing stableIds are preserved.

One panel is added: Upstream failure share by format, a ratio over the three existing *_remote_upstream_responses_total families grouping server_error|transport_error, so the health row carries an upstream signal. No new metrics.

Rendered copy for review: https://dashboards.gitlab.net/d/jpereira-verify-ar-remote