es搜索字段大小写不敏感

需求
username字段类型为keyword，需要实现termQuery username时，大小写不敏感

settings设置如下

{
    "index": {
        "routing": {
            "allocation": {
                "total_shards_per_node": "2"
            }
        },
        "refresh_interval": "1s",
        "number_of_shards": "5",
        "number_of_replicas": "1"
    },
    "analysis": {
        "normalizer": {
            "lowercase": {
                "filter": [
                    "lowercase"
                ],
                "type": "custom"
            }
        }
    }
}

mappings设置如下

{
    "properties": {
        "username": {
            "normalizer": "lowercase",
            "type": "keyword"
        }
    }
}