fix(validation): make uploaded dashboard smoke runs practical on spaces with many dashboards

[shmsr]

Summary

grafana-validate-uploaded can appear hung when run without --dashboard-id or --dashboard-title in a busy Kibana space. In the Serverless test space it attempted to inspect all ~200 dashboard saved objects, including many [DELETED] placeholders, before writing any report.

Evidence

Command run:

grafana-validate-uploaded \
  --kibana-url "$KIBANA_ENDPOINT" \
  --kibana-api-key "$KEY" \
  --es-url "$ELASTICSEARCH_ENDPOINT" \
  --es-api-key "$KEY" \
  --output /tmp/.../uploaded_dashboard_smoke_report.json \
  --timeout 60 \
  --fail-on-runtime-errors \
  --fail-on-layout-issues \
  --fail-on-empty-panels \
  --fail-on-not-runtime-checked

It produced no report after ~5 minutes and was stopped. A follow-up dashboard listing showed 200 dashboards, including placeholders.

Expected

The validator should be practical for migration runs:

• encourage or support validating dashboards from a migration artifact/upload result,
• print progress before the final report,
• optionally skip [DELETED] placeholder dashboards by default,
• make unscoped all-space validation explicit in the output.