Fix contradictory debug messages in influxdb output

[reimda]

When telegraf is configured to print debug level errors and the influxdb output is begin used, if there is a server error (or any HTTP 4xx response), telegraf prints two debug messages that contradict each other:

2022-10-04T22:20:23Z E! [outputs.influxdb] E! [outputs.influxdb] Failed to write metric (will be dropped: 401 Unauthorized):
2022-10-04T22:20:23Z D! [outputs.influxdb] Wrote batch of 15 metrics in 6.440209ms

The first one says metrics were dropped, the second says they were written.

Since the RunningOutput only prints the "Wrote batch" message when there's no error, maybe the output shouldn't return nil here

telegraf/plugins/outputs/influxdb/http.go

Line 390 in bc2b328

return nil

and maybe it should return an APIError like it does for other cases:

telegraf/plugins/outputs/influxdb/http.go

Line 431 in bc2b328

return &APIError{

[reimda]

I'm working on a PR for this