Add support to run pre-execution queries such as SET statements for runtime configurations

[jsjasonseba]

Describe your feature request

Please describe the behavior you want and the motivation.

Related to: #645 #656 #512

Several use cases require issuing SET statement, such as setting transaction isolation levels, timeouts, etc. Connectorx can support this use case by adding a new parameter pre_execution_querries on cx.read_sql where user can submit SET statements and it is run before the SELECT statement. Since SET statements are typically applied per session (connection), each connection created for each partition must execute the pre-execution queries after connection is created.

I’m currently developing this functionality and planning to submit a PR. But I'm not certain if this aligns with the project’s direction. Any feedback or discussion would be appreciated.