Update changelog

(cherry picked from commit e31b781)

CHANGELOG.md

@@ -2,6 +2,25 @@
 
 # Change Log
 
+## v1.21.0-rc1 [2021-12-08]
+
+### Bugfixes
+
+   - [#10196](https://github.com/influxdata/telegraf/pull/10196) `outputs.elasticsearch` Implement NaN and inf handling fo     r elasticsearch output
+   - [#10205](https://github.com/influxdata/telegraf/pull/10205) Print loaded plugins and deprecations for once and test f     lags
+   - [#10214](https://github.com/influxdata/telegraf/pull/10214) `processors.ifname` Eliminate MIB dependency for ifname p     rocessor
+   - [#10206](https://github.com/influxdata/telegraf/pull/10206) `inputs.snmp` Optimize locking for SNMP MIBs loading
+   - [#9975](https://github.com/influxdata/telegraf/pull/9975) `inputs.kube_inventory` Set TLS server name config properly
+   - [#10230](https://github.com/influxdata/telegraf/pull/10230) Sudden close of Telegraf caused by OPC UA input plugin
+   - [#9913](https://github.com/influxdata/telegraf/pull/9913) Update github.com/eclipse/paho.mqtt.golang module from 1.3.     0 to 1.3.5
+   - [#10221](https://github.com/influxdata/telegraf/pull/10221) `parsers.json_v2` Parser timestamp setting order
+   - [#10209](https://github.com/influxdata/telegraf/pull/10209) `outputs.graylog` Ensure graylog spec fields not prefixed      with _
+   - [#10099](https://github.com/influxdata/telegraf/pull/10099) `inputs.zfs` Pool detection and metrics gathering for ZFS      >= 2.1.x
+   - [#10007](https://github.com/influxdata/telegraf/pull/10007) `processors.ifname` Parallelism fix for ifname processor
+   - [#10208](https://github.com/influxdata/telegraf/pull/10208) `inputs.mqtt_consumer` Mqtt topic extracting no longer re     quires all three fields
+   - [#9616](https://github.com/influxdata/telegraf/pull/9616) Windows Service - graceful shutdown of telegraf
+   - [#10203](https://github.com/influxdata/telegraf/pull/10203) Revert unintented corruption of the Makefile  
+
 ## v1.21.0-rc0 [2021-12-01]
 
 ### Release Notes

etc/telegraf.conf

@@ -676,6 +676,15 @@
 #   ## If set to true a unique ID hash will be sent as sha256(concat(timestamp,measurement,series-hash)) string
 #   ## it will enable data resend and update metric points avoiding duplicated metrics with diferent id's
 #   force_document_id = false
+#
+#   ## Specifies the handling of NaN and Inf values.
+#   ## This option can have the following values:
+#   ##    none    -- do not modify field-values (default); will produce an error if NaNs or infs are encountered
+#   ##    drop    -- drop fields containing NaNs or infs
+#   ##    replace -- replace with the value in "float_replacement_value" (default: 0.0)
+#   ##               NaNs and inf will be replaced with the given number, -inf with the negative of that number
+#   # float_handling = "none"
+#   # float_replacement_value = 0.0
 
 
 # # Configuration for Event Hubs output plugin