Add logging to integration test config request

[mikewilli]

CI was failing on #11243 for one of the integration tests (Test SDK Targeting (Release Firefox)), and it appears to have been a timing issue that resolved itself. However, we should add more logging to the JSON decoding so that we can more easily diagnose this if it pops up again.

I think we would want to include what the failing JSON object is in the except block here https://github.com/mozilla/experimenter/blob/main/experimenter/tests/integration/nimbus/utils/helpers.py#L25-L27.

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