Add allow_nan_equality option to assert_approx_df_equality

[mitches-got-glitches]

I feel like this would be quite useful. Were there any design choices for why it wasn't included or would this be a useful addition?

https://github.com/MrPowers/chispa/blob/500793efe14b1975b86fb1a923ee6cd68ba559d8/chispa/dataframe_comparer.py#L38-L40

[MrPowers]

@mitches-got-glitches - yea, allow_nan_equality is probably even more important for assert_approx_df_equality. Feel up for sending me a PR?

[mitches-got-glitches]

Hi @MrPowers , yes I will have a go this week! Cheers

[MrPowers]

Awesome, thanks @mitches-got-glitches!