[dashboard] Rework dashboard (MIG support, Grafana deprecations, Host…

…name)

* Use PromQL aggregations to take MIG subdevices into account (see #353)
* Update all panels to use Timeseries panels (instead of deprecated Graph)
* Switch from instance to Hostname to select individual systems to avoid
  duplicated timeseries for Kubernetes daemonsets and their Pod names
* Use DCGM_FI_DEV_FB_FREE instead of DCGM_FI_DEV_GPU_TEMP to also cover vGPU (~ PR #240)
* Use DCGM_FI_PROF_GR_ENGINE_ACTIVE to determine utilization to cover MIG (and vGPU)

Fixes: #353, #236

Signed-off-by: Christian Rohmann <[email protected]>