c/driver_manager: support vendoring somehow

[lidavidm]

What feature or improvement would you like to see?

This is useful when embedding the driver manager as an extension into some other system, where there may be multiple extensions that want to use the driver manager (e.g. imagine a DuckDB extension, or plugging ADBC into a SQL editor or BI tool). Being able to vendor the driver manager would make development easier and avoid potential runtime conflicts/multiple definition errors. We could imitate Nanoarrow and provide a build parameter + macros that add a chosen prefix to all driver manager names or wrap all symbols in a given C++ namespace.