hotfix: add data retention to system buckets, add user defined tags to system buckets, closes influxdata/DAR#158

content/influxdb/v2.0/reference/internals/system-buckets.md

@@ -36,6 +36,8 @@ For more information, see [InfluxDB key concepts](/influxdb/v2.0/reference/key-c
 The `_monitoring` system bucket stores InfluxDB data used to
 [monitor data and send alerts](/influxdb/v2.0/monitor-alert/).
 
+**Data retention:** 7 days
+
 ### \_monitoring bucket schema
 
 - **statuses** _(measurement)_
@@ -45,7 +47,7 @@ The `_monitoring` system bucket stores InfluxDB data used to
         - **\_level:** level evaluated by the check (ok, info, warn, or crit)
         - **\_source\_measurement:** original measurement queried by the check
         - **\_type:** check type (threshold or deadman)
-        - _other tags inherited from queried data_
+        - _other tags inherited from queried data or added in the check configuration_
     - **fields:**
         - **\_message:** message generated by the check
         - **\_source_timestamp:** original timestamp of the queried data
@@ -62,7 +64,7 @@ The `_monitoring` system bucket stores InfluxDB data used to
         - **\_sent:** sent status (true or false)
         - **\_source\_measurement:** original measurement queried by the check
         - **\_type:** check type (threshold or deadman)
-        - _other tags inherited from queried data_
+        - _other tags inherited from queried data or added in the check configuration_
     - **fields:**
         - **\_message:** message generated by the check
         - **\_source_timestamp:** original timestamp of the queried data
@@ -72,6 +74,8 @@ The `_monitoring` system bucket stores InfluxDB data used to
 ## \_tasks system bucket
 The `_tasks` system bucket stores data related to [InfluxDB task](/influxdb/v2.0/process-data/) executions.
 
+**Data retention:** 3 days
+
 ### \_tasks bucket schema
 
 _A **task run** refers to a single task execution._