[Metrics UI] [Regression] Host Details page only shows CPU Usage box

[Zacqary]

Kibana version:
7.10, 7.11

Starting in 7.10, the only box that shows up at the top of this page is the one for "CPU Usage," even though the page is displaying multiple other metrics.

Kubernetes pods are unaffected. Haven't tested other node types yet, but this may only be happening for Hosts.

[elasticmachine]

Pinging @elastic/logs-metrics-ui (Team:logs-metrics-ui)

[simianhacker]

@estermv and I debugged this issue and discovered that TSVB changed the response for gauge type requests to only return 1 series instead of the multiple series requested. If we change all the type attributes on the TSVB inventory models from gauge to top_n it works as expected. We also discussed adding an integration test under x-pack/test/api_integration/metrics_ui/metrics.ts for hostSystemOverview to ensure it returns the correct number of series in the response.