Prepare client for HTTP 202 Accepted

[nhoening]

What we propose in FlexMeasures/flexmeasures#2170 is a breaking change for the FlexMeasures client, which runs check_for_status(status, 200). I believe check_for_status'() should accept more than one admissible status, so we can make the client robust against prevoius FM server versions.

Make this change early on. A new client release would then already prepare for the FlexMeasures release that switches to 202.

[Flix6x]

I advise to accept all 2xx status codes and log (info or debug, whatever is appropriate) accordingly.