Support InfluxDB 3

[adubovik]

1. The analytics code that writes raw datapoints to InfluxDB 2 requires no changes, since InfluxDB 3 supports /api/v2/write endpoint via which InfluxDB 2 client makes writes.
2. The configuration env variables change meaning slightly:

   Variable	InfluxDB 2	InfluxDB 3
   INFLUX_URL	URL to the InfluxDB 2 to write the analytics data	URL to the InfluxDB 3 to write the analytics data
   INFLUX_ORG	Name of the InfluxDB organization to write the analytics data	Ignored by InfluxDB 3; could be set to any value
   INFLUX_BUCKET	Name of the InfluxDB 2 bucket to write the analytics data	Name of the InfluxDB 3 database to write the analytics data
   INFLUX_API_TOKEN	InfluxDB 2 API Token	InfluxDB 3 API Token with the write access to the target database

3. The dashboards should be rewritten from scratch, since InfluxDB 3 doesn't support Flex query language anymore.
4. The ETL task templates should be rewritten from scratch probably using InfluxDB plug-ins.
5. Provide a script to migrate timeseries from InfluxDB 2 to InfluxDB 3.