M16.6 Custom dashboards like Grafana #69

Part of #63. Needs M16.3.

yuva-api

• monitor_dashboards per workspace with a MonitorDashboardDocument (schema: 1): time range, auto-refresh, up to 10 variables (property, route, consumer, environment, service, custom), up to 50 panels on a 24-column grid with up to 5 queries each (the query operation's own body over traffic, support, api, uptime or health), chart type (time series, bar, table, stat, gauge, latency heatmap, health, text), unit, thresholds; a version for concurrent edits.
• A threshold on an api, uptime or health metric becomes an M16.4 alert rule.
• Dashboards in /v1, import and export as the document; starter dashboards for an API, a website and an app shipped in the binary.
• Dashboard share links through analytics_shares with dashboard_id, fixed variable values and the properties named at share time.
• /prometheus/api/v1/ query, query_range, labels, label/{name}/values, series, status/buildinfo for keys with analytics:read: the yuva_* gauge series, selectors with =, !=, =~, !~, sum|avg|min|max|count by|without, topk, bottomk, arithmetic with literals and between like-labelled vectors, number literals; compiled to one query (duration aggregations merge sketches); 400 bad_data for range vectors, rate, histogram_quantile and the rest; steps of at least 60 s, at most 11,000 points.

yuva-panel

• Dashboard editor: add, resize and move panels, a query builder, chart settings, variables, time picker, auto-refresh, full-screen (TV) mode, starter dashboards, share links. en and tr.

yuva-docs

• Building dashboards, connecting Grafana, the supported PromQL subset with examples; en, tr, de.

Done when

A dashboard built in the editor shows the same numbers as the fixed API and analytics views for the same filter; it survives export and import; a dashboard share link shows only its fixed variable values; Grafana (a pinned release in CI) with the Yuva data source passes its data-source test and draws the same series.