feat(httpx): implement optional body logging also on http error (#651)

1. we want optionally to log the body (we don't want to log the body
when we're fetching psiphon secrets or tor targets)

2. we want body logging to _also_ happen on error since this is quite
useful to debug possible errors when accessing the API

This diff adds the above functionality, which were previously
described in https://github.com/ooni/probe/issues/1951.

This diff also adds comprehensive testing.

internal/engine/geolocate/ipinfo.go

@@ -26,7 +26,7 @@ func ipInfoIPLookup(
 		HTTPClient: httpClient,
 		Logger:     logger,
 		UserAgent:  httpheader.CLIUserAgent(), // we must be a CLI client
-	}).Build().GetJSON(ctx, "/", &v)
+	}).WithBodyLogging().Build().GetJSON(ctx, "/", &v)
 	if err != nil {
 		return DefaultProbeIP, err
 	}