Optional flag to close query with flush

[hongker]

#1271

Summary

• feature: close query and release connection when use batch.Flush()
• usage:

batch, err := conn.PrepareBatch(ctx, "INSERT INTO some_table", driver.WithCloseQuery())

for {
   // other append code
   if err = batch.Flush(); err != nil {
        break
   }
}

Checklist

Delete items not relevant to your PR:

• Unit and integration tests covering the common scenarios were added
• A human-readable description of the changes was provided to include in CHANGELOG
• For significant changes, documentation in https://github.com/ClickHouse/clickhouse-docs was updated with further explanations or tutorials

[CLAassistant]

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1 out of 2 committers have signed the CLA.

✅ jkaflik
❌ colincchen

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[hongker]

@jkaflik What do I still need to do for this pr?

[jkaflik]

@hongker it's pending my review.