Retry on network errors and fix retries on async inserts with `database/sql` interface

[tommyzli]

Summary

This PR fixes two issues with the database/sql interface

1. The async insert code path is missing a check to signal a retry (by returning driver.ErrBadConn) if the connection is broken
2. isConnBrokenError is to restrictive. The postgres driver marks all net.OpErrors as BadConns so I applied that here too

Checklist

Delete items not relevant to your PR:

• [x] 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

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