chore(exporter): improve logging when fetching relays-data

see: BEDS-90

backend/pkg/exporter/modules/relays.go

@@ -114,15 +114,15 @@ func fetchDeliveredPayloads(r types.Relay, offset uint64) ([]BidTrace, error) {
 
 	if err != nil {
 		log.Error(err, "error retrieving delivered payloads", 0, map[string]interface{}{"relay": r.ID})
-		return nil, err
+		return nil, fmt.Errorf("error retrieving delivered payloads for cursor: %v, url: %v: %v", offset, url, err)
 	}
 
 	defer resp.Body.Close()
 
 	err = json.NewDecoder(resp.Body).Decode(&payloads)
 
 	if err != nil {
-		return nil, err
+		return nil, fmt.Errorf("error decoding json for delivered payloads for cursor: %v, url: %v: %v", offset, url, err)
 	}
 
 	return payloads, nil
@@ -176,7 +176,7 @@ func retrieveAndInsertPayloadsFromRelay(r types.Relay, low_bound uint64, high_bo
 	for {
 		resp, err := fetchDeliveredPayloads(r, offset)
 		if err != nil {
-			return err
+			return fmt.Errorf("error calling fetchDeliveredPayloads with offset: %v for relay: %v", r.ID, err)
 		}
 
 		if resp == nil {