feat: support MySQL database connections

[mattjohnsonpint]

Description

Add support for MySQL database connections.

❗ Note: This includes some minor breaking changes to the Modus Go SDK for existing database query APIs for PostgreSQL, which are shared now for both PostgreSQL and MySQL. Specifically, return types for Execute, Query, and QueryScalar have been updated to return structs. Calling code should be updated accordingly. See the examples for details.

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