Add tagexclude functionality for the database_tag property in the InfluxDB Output Plugin

[amarbajric]

Feature Request

The InfluxDB v1.x Output Plugin currently allows to add a database_tag configuration property that dynamically routes data into the specified database. The tag that is used for dynamically routing data into the correct database (i.e. database_tag) cannot be removed by telegraf (for example with tagexclude)

See the following comment of this PR for more information.

Proposal:

Implement/Add a functionality for excluding the tag specified in database_tag before telegraf writes data to influxdb as this tag is, most of the time, only needed for routing data to the correct database.

To avoid future feature requests, the same functionality would also be helpful for the InfluxDB v2.x Output Plugin and the bucket_tag configuration property.

Current behavior:

Data is dynamically routed based on the database_tag but cannot be excluded before data is written to influxdb.

Desired behavior:

The database_tag should be removable by using something like the already known functionality of tagexclude or an additional configuration parameter like exclude_database_tag=true|false etc.

Use case:

There are many use cases where dynamic routing based on the database_tag is desired without storing the specified tag of database_tag into the database (i.e. tag is only used for routing purposes and has no information value)