More flexible Json_Date_Format

Clickhouse is pretty strict on data formats and fails to parse "2018-10-13T17:46:23.000000Z" which is generated by json_date_format iso8601. So, as far as I understand, the only way to fix this is to create a proxy server which will convert this format to Clickhouse supported "2016-06-15 00:11:21". It would be helpful to do it on the fluentbit output plugin level.