allow url parameters in query configuration

[piif]

Aggregation query results may be polluted by extra fields which implies many useless metrics. To filter there fields, one may use ?filter_path= parameters to url. Thus a query configuration options should be usefull to add this query string on called URL.

[piif]

here is an example : with following aggregator, the exporter will return my_query_le_doc_count and my_query_le_to :

            "aggs": {
              "le": {
                  "range": {
                    "field": "time_request",
                    "ranges": [
                        { "to":    "1", "key":    "1" },
                        { "to":    "10", "key":    "10" },
                        { "to":    "100", "key":    "100" },
                        { "from":    "100", "key":    "+Inf" }
                  ]
                }
              }

Metric my_query_le_doc_count may be use as an histogram metric and quantile function works directly on it On the other hand, metric my_query_le_to is useless, thus i may appe,nd to the url ?filter_path=aggregations.le.buckets.key,aggregations.le.buckets.doc_count to filter out "to" field. But the exporter has no way to specify this parameter