Extend /sql/:id/queries to return result set metadata

The GUI needs result set metadata like column datatypes, sizes, and the result set's table name to add the "Export as SQL" option. Parsing the query in the GUI was considered but it's not an optimal approach as the users can have multiple "select" in a stored procedure, the GUI can't parse the store procedure to query additional metadata.
The `mariadb-connector-cpp` seems to have the `ResultSetMetaData` interface, so getting the result set's metadata seems possible.