grafana: the data-transferred-by-domain panel steps at 5 minutes and draws bars

Squid logs a tunnel's bytes once, when it closes, so a large download was
one point in a small bucket and read as instantaneous. The panel now has a
5 minute minimum interval and bars, so that point is a visible bar. The
module-eval check pins both.

nix/host-modules/swarm-grafana/dashboards/egress.json

@@ -1589,7 +1589,7 @@
         "spec": {
           "id": 21,
           "title": "Data transferred by domain over time",
-          "description": "Bytes per top-10 domain, rest as other. A tunnel is logged at close, so long ones spike.",
+          "description": "Bytes per top-10 domain, rest as other, in 5 minute bars. A tunnel counts when it closes.",
           "links": [],
           "data": {
             "kind": "QueryGroup",
@@ -1637,7 +1637,9 @@
                 }
               ],
               "transformations": [],
-              "queryOptions": {}
+              "queryOptions": {
+                "interval": "5m"
+              }
             }
           },
           "vizConfig": {
@@ -1663,9 +1665,9 @@
                     "mode": "palette-classic"
                   },
                   "custom": {
-                    "drawStyle": "line",
+                    "drawStyle": "bars",
                     "lineWidth": 1,
-                    "fillOpacity": 10,
+                    "fillOpacity": 60,
                     "showPoints": "never",
                     "spanNulls": false,
                     "axisSoftMin": 0