dashboard: add panels for CRUD module statistics

Statistics for CRUD module was introduced in CRUD 0.11.0 [1].
To enable statistics integrated with metrics with quantiles, call

  crud.cfg{
      stats = true,
      stats_driver = 'metrics',
      stats_quantiles = true
  }

This patch adds panels for
- tnt_crud_stats summary (+ tnt_crud_stats_count, tnt_crud_stats_sum)
- tnt_crud_tuples_fetched
- tnt_crud_tuples_lookup
- tnt_crud_map_reduces

CRUD panels are stored in "CRUD module statistics" section.
There is a group of panels for RPS load and a group of panels with
latency, both consists of separate panels for each operation
and ok/error status. Tuples panels are displayed as average per request.
InfluxDB queries for tuple panels have minor issue: they can show
0 current value from time to time due to `fill(0)` and `GROUP BY`
including partial intervals [2]. Map reduces panel show average RPS.

1. https://github.com/tarantool/crud/releases/tag/0.11.0
2. influxdata/influxdb#8244

Closes #143

CHANGELOG.md

@@ -7,6 +7,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ## Unreleased
 
 ### Added
+- Panels for CRUD module statistics
 
 ### Changed
 - Set default InfluxDB policy to `autogen`

dashboard/influxdb_dashboard.libsonnet

@@ -118,4 +118,10 @@ dashboard.new(
     policy=variable.influxdb.policy,
     measurement=variable.influxdb.measurement,
   )
+).addPanels(
+  section.crud(
+    datasource=variable.datasource.influxdb,
+    policy=variable.influxdb.policy,
+    measurement=variable.influxdb.measurement,
+  )
 )

dashboard/panels/common.libsonnet

@@ -96,4 +96,18 @@ local prometheus = grafana.prometheus;
       std.join('\n\n', [description, "If `No data` displayed, check up your 'rate_time_range' variable."])
     else
       description,
+
+  group_by_fill_0_warning(
+    description,
+    datasource='${DS_INFLUXDB}'
+  )::
+    if datasource == '${DS_INFLUXDB}' then
+      std.join('\n', [description, |||
+        Current value may be 0 from time to time due to fill(0)
+        and GROUP BY including partial intervals.
+        Refer to https://github.com/influxdata/influxdb/issues/8244
+        for updates.
+      |||])
+    else
+      description,
 }