PERF: enable nullable integer for read_sql via parameter
Function `pandas.read_sql` read SQL query or database table into a DataFrame. However, for nullable integer columns, once there exists one row with null, pandas will infer this column as float, which may lead to subsequent issues (in our case, we use DataFrame for ETL and the integer converted to float, not suitable for our sink database table schema).
Using nullable integer is one of the solution we adopted, which may cause more memory usage. Therefore, I add default False parameter for `pandas.read_sql` to not enable it as default, once you want to enable it, just set it as True.