(fleet/grafana-dashboards) add heatmaps/histrograms to Deliverator Summary dash

New visualizations:
  - Total Duration: Successful
  - Total Duration: Failed
  - Transfer Duration: Successful
  - Transfer Duration: Failed
  - Effective Transfer Rate Per File
  - File Size: Successful
  - File Size: Failed
  - Queued Duration: Successful
  - Queued Duration: Failed

Note that both of the Queued Duration visualizations are unreliable for
as yet unknown reasons.

Author: jhoblitt