DbalExecutor depends on concrete connection

[ro0NL]

See #906 (comment) for background.

We currently copy/pasted DbalExecutor to handle ALTER queries via Percona Toolkit: https://docs.percona.com/percona-toolkit/pt-online-schema-change.html

The copy/paste broke today due updated upstream.

Ideally we pass a decorated connection to DbalExecutor, to handle ALTER queries as such.