I've used telegraf a bit in the past, and I know it has plugins for everything. but as far as I am aware, none of them are required.
Yes it is required to have an upstream db, but apart from that you can configure anything. It's a monitoring app, it will monitor what you tell it to, and report it upstream.

For me this is really a question of why is telegraf dependant on Mosquitto ? It may just be used to monitor docker ?