Add support for case-changing functions

[galkk]

Implement support for case-changing functions

As per #123, there is no support for case change functions in SQL.

Implement custom script functions that will do that (SQLFunctions.java)

Reference

• https://www.elastic.co/guide/en/elasticsearch/reference/current/sql-functions-string.html#sql-functions-string-lcase

• https://www.elastic.co/guide/en/elasticsearch/reference/current/sql-functions-string.html#sql-functions-string-ucase

[galkk]

This is a sketch of how the potential solution might look like

POST /kibana_sample_data_logs/_search
{
  "from": 0,
  "size": 200,
  "query": {
    "bool": {
      "filter": [
        {
          "bool": {
            "must": [
              {
                "script": {
                  
                  "script": {
                    "source": "doc['host.keyword'].value == params.v0.toLowerCase()",
                    "lang": "painless",
                    "params" : {
                      "v0": "WWW.ELASTIC.CO"
                    }
                  },
                  "boost": 1
                }
              }
            ],
            "adjust_pure_negative": true,
            "boost": 1
          }
        }
      ],
      "adjust_pure_negative": true,
      "boost": 1
    }
  },
  "_source": {
    "includes": [
      "host"
    ],
    "excludes": []
  }
}