Parse large floats in CSVs that have periods as the thousands separator

[matterhorn103]

Description

It's great to see that polars now supports reading from CSV files where the decimal separator is a comma, thanks for that!

Unfortunately, in the countries where usage of a decimal comma is common, you frequently encounter the period used as a thousands separator e.g. 1.299,99, and read_csv() (and I assume scan_csv() too) doesn't currently cope with this.

It would be nice to be able to specify a thousands separator, or to simply automatically parse . as a thousands separator when the user has passed decimal_comma=True.