Add support for Telegraf's ability to pull remote configurations

[samhld]

Describe the issue here:
InfluxDB 2.X users will hopefully be taking advantage of the feature that allows for storing Telegraf configurations centrally in their InfluxDB instance. Telegraf currently supports pulling its configuration from a URL so it can grab these configs.

Since this is tooling designed to automate the deployment and configuration of Telegraf, I imagine supporting this form of pulling configuration will be desired for the operator as well.

Obviously this operator is in its very early stages so I have no data to back up this hypothesis but figured I'd log this in case others felt it would be a necessary addition as well!

[BondAnthony]

I think this would be a really good integration, here are my thoughts.

Users would need to supply the telegraf url as an annotation or we can allow a number of new annotations and build the url. The telegraf sidecar would need to include the INFLUX_TOKEN variable so telegraf could pull the configuration with the --config flag. I think pulling from cloud for each container startup would be a little intensive. It's possible we could pull the configuration once then store as a configmap. Currently cloud doesn't support editing these configurations but we should support an update process.

/cc @wojciechka