feat(inputs.redis): Add additional commandstat fields (#13866)

plugins/inputs/redis/README.md

@@ -148,8 +148,10 @@ and the elapsed time since the last rdb save (rdb\_last\_save\_time\_elapsed).
   - avg_ttl(int, number)
 
 - redis_cmdstat
-    Every Redis used command will have 3 new fields:
+    Every Redis used command could have the following fields:
   - calls(int, number)
+  - failed_calls(int, number)
+  - rejected_calls(int, number)
   - usec(int, mircoseconds)
   - usec_per_call(float, microseconds)
 
@@ -169,7 +171,7 @@ and the elapsed time since the last rdb save (rdb\_last\_save\_time\_elapsed).
     - err
   - fields:
     - total (int, number)
-  
+
 ### Tags
 
 - All measurements have the following tags:
@@ -221,7 +223,7 @@ redis_keyspace,database=db1,host=host,server=localhost,port=6379,replication_rol
 redis_command:
 
 ```text
-redis_cmdstat,command=publish,host=host,port=6379,replication_role=master,server=localhost calls=68113i,usec=325146i,usec_per_call=4.77 1559227136000000000
+redis_cmdstat,command=publish,host=host,port=6379,replication_role=master,server=localhost calls=569514i,failed_calls=0i,rejected_calls=0i,usec=9916334i,usec_per_call=17.41 1559227136000000000
 ```
 
 redis_error:

plugins/inputs/redis/redis.go

@@ -541,7 +541,7 @@ func gatherCommandstateLine(
 		switch kv[0] {
 		case "calls":
 			fallthrough
-		case "usec":
+		case "usec", "rejected_calls", "failed_calls":
 			ival, err := strconv.ParseInt(kv[1], 10, 64)
 			if err == nil {
 				fields[kv[0]] = ival

plugins/inputs/redis/redis_test.go

@@ -248,6 +248,16 @@ func TestRedis_ParseMetrics(t *testing.T) {
 	}
 	acc.AssertContainsTaggedFields(t, "redis_cmdstat", cmdstatCommandFields, cmdstatCommandTags)
 
+	cmdstatPublishTags := map[string]string{"host": "redis.net", "replication_role": "master", "command": "publish"}
+	cmdstatPublishFields := map[string]interface{}{
+		"calls":          int64(488662),
+		"usec":           int64(8573493),
+		"usec_per_call":  float64(17.54),
+		"rejected_calls": int64(0),
+		"failed_calls":   int64(0),
+	}
+	acc.AssertContainsTaggedFields(t, "redis_cmdstat", cmdstatPublishFields, cmdstatPublishTags)
+
 	replicationTags := map[string]string{
 		"host":             "redis.net",
 		"replication_role": "slave",
@@ -518,6 +528,7 @@ cluster_enabled:0
 # Commandstats
 cmdstat_set:calls=261265,usec=1634157,usec_per_call=6.25
 cmdstat_command:calls=1,usec=990,usec_per_call=990.00
+cmdstat_publish:calls=488662,usec=8573493,usec_per_call=17.54,rejected_calls=0,failed_calls=0
 
 # Errorstats
 errorstat_CLUSTERDOWN:count=8