Capture the AG listener names

[billgraziano]

mssql_ag_listeners = a,b,c

Send this as a string array so it goes as a JSON array object

"logstash.tags": [
      "input.json.tcp.6514",
      "kcinf.lssip02p",
      "ingest.json",
      "kcinf.lsindx01p",
      "index.sql",
      "600-xelogstash.erb",
      "800-globals.erb"
    ],

"mssql_ag_listeners":[
  "Listener1",
  "Listener2"
],