Including the MQTT topic as tag or not

[keomabrun]

Feature Request

Hey! Thank you for the awesome work. I am using this plugin and I like it very much.

Could it be possible to decide whether the topic is saved as a tag or not ?

Proposal:

Current behavior:

Currently, the topic is saved as a tag in Influxdb and it produces a lot of different series.
https://github.com/influxdata/telegraf/tree/master/plugins/inputs/mqtt_consumer#metrics

As stated in the Influx document, creating too many series will increase memory usage:
https://docs.influxdata.com/influxdb/v1.7/concepts/schema_and_data_layout/#don-t-have-too-many-series

Desired behavior:

Could it be possible to let the user decide whether they want the topic to be saved as a tag or not ?

Use case:

I don't use the information contained in the topic after the data is saved in InfluxDB so I would like to remove the topics from the tags list.

[keomabrun]

Wow ! That was fast. Thanks !