I have the following .conf file for Logstash:

```
input {
    file {
        path => "C:/elastic/logstash-8.3.2/config/*.csv"
        start_position => "beginning"
        sincedb_path => "NULL"
    }
}
filter {
    csv {
        separator => ";"
        columns => ["name","deposit","month"]
    }
    mutate {
        convert => {
            "deposit" => "integer"
        }
    }
}
output {
    elasticsearch {
        hosts => "http://localhost:9200"
        index => "payment_test"
    }
    stdout {}
}

```

I get inputs from 10 .csv files, which have names like `in-0.csv`, `in-1.csv` and so on. I want the index names in ElasticSearch to be `payment_test-0`, `payment_test-1` and so on for the corresponding .csv input files (the data in `in-0.csv` would be in index `payment_test-0` and so on). How can I achieve this?