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/probeservices/measurementmeta.go

@@ -59,7 +59,7 @@ func (c Client) GetMeasurementMeta(
 		HTTPClient: c.HTTPClient,
 		Logger:     c.Logger,
 		UserAgent:  c.UserAgent,
-	}).Build().GetJSONWithQuery(ctx, "/api/v1/measurement_meta", query, &response)
+	}).WithBodyLogging().Build().GetJSONWithQuery(ctx, "/api/v1/measurement_meta", query, &response)
 	if err != nil {
 		return nil, err
 	}