Json values with ULL suffix

[DifferentialOrange]

Some metrics parse their values to ULL strings:

[{
   "label_pairs":{
      "engine":"memtx",
      "name":"MY_SPACE",
      "alias":"tnt_router"
   },
   "timestamp":1635867200499883,
   "metric_name":"tnt_space_bsize",
   "value":"51589ULL"
},
{
   "label_pairs":{
      "engine":"memtx",
      "name":"MY_SPACE",
      "alias":"tnt_router"
   },
   "timestamp":1635867200499883,
   "metric_name":"tnt_space_total_bsize",
   "value":"199045ULL"
}]

This values can't be parsed by Telegraf+InfluxDB monitoring stack. This issue was already solved for Prometheus (#15) and Graphite (#90), but not for json.