Dashboard: Loki Operational improvements (#2041)

* fixing indentation so I can see diffs better

Signed-off-by: Ed Welch <edward.welch@grafana.com>

* add rows for chunks, streams, dropped samples.
success rate graphs now only look at 5xx errors (4xx are considered "successful")
Limited the mouseover to only show the active line for a bunch of graphs.

Signed-off-by: Ed Welch <edward.welch@grafana.com>