Update SQL docs (#1645)

* Update SQL schema reading docs: migrate schema methods to `DataFrameSchema`

Adjusted documentation to reflect changes introduced in `Beta-4`, moving schema-related methods from `DataFrame` to `DataFrameSchema` companion object. Added examples leveraging `DataSource` for connection pooling and HikariCP usage.

* Expand `DbType` documentation with advanced customization methods

Updated the documentation to include new advanced customization options for the `DbType` class, covering performance settings, query building, connection handling, and type mapping. Added detailed explanations and examples for overriding methods and properties.

* Clarify SQL method descriptions and adjust grammar in documentation

Author: zaleslaw