Add where clause support for covering index

[dai-chen]

Description

1. Support WHERE clause CREATE INDEX statement for partial indexing. Only source data matched the given filtering condition will be processed.
2. Add empty implementation for create skipping index statement. Because filtering condition support may impact skipping index query rewrite (covering index doesn't have this feature) and thus need more time. Added the grammar now so PPL plugin can includes it first.

Example

spark-sql> CREATE INDEX client_status_idx ON ds_tables.http_logs
         > (clientip, status)
         > WHERE status != 200
         > WITH (
         >   auto_refresh = true
         > );

GET flint_myglue_ds_tables_http_logs_client_status_idx_index/_mapping
{
  "flint_myglue_ds_tables_http_logs_client_status_idx_index": {
    "mappings": {
      "_meta": {
        "kind": "covering",
        "indexedColumns": [
          {
            "columnType": "string",
            "columnName": "clientip"
          },
          {
            "columnType": "int",
            "columnName": "status"
          }
        ],
        "name": "client_status_idx",
        "options": {
          "auto_refresh": "true"
        },
        "source": "myglue.ds_tables.http_logs",
        "version": "0.1.0",
        "properties": {
          "filterCondition": "status != 200"
        }
      },
      "properties": {
        "clientip": {
          "type": "keyword"
        },
        "status": {
          "type": "integer"
        }
      }
    }
  }
}

GET flint_myglue_ds_tables_http_logs_client_status_idx_index/_search
{
    ......
    "hits": [
      {
        "_index": "flint_myglue_ds_tables_http_logs_client_status_idx_index",
        "_id": "kyUjaIsBWdGHpYUCCTv-",
        "_score": 1,
        "_source": {
          "clientip": "107.8.3.0",
          "status": 304
        }
      },
      {
        "_index": "flint_myglue_ds_tables_http_logs_client_status_idx_index",
        "_id": "liUjaIsBWdGHpYUCCTv-",
        "_score": 1,
        "_source": {
          "clientip": "250.126.5.0",
          "status": 304
        }
      },

Issues Resolved

#23, #89

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