Handling datetime generation

[DaveBrind-zz]

At the moment SDMETRICS gives many warnings originating from line 40 in their utils file https://github.com/sdv-dev/SDMetrics/blob/master/sdmetrics/utils.py. This function calculates frequencies of values in original data & synthetic data and throws warnings when values in synthetic data cannot be found in the real data.

It seems to do this a lot for datetime columns and this is probably due to the generation calculating them down to the smallest unit of time. Need to look at potentially truncating datetime columns to match whatever the unit in the input column is.

At the moment this is just handled by suppressing the warnings.