[FEA] Allow quantile(0.5) to behave like median and not always return float

[mroeschke]

Is your feature request related to a problem? Please describe.

In [1]: from cudf import *

In [2]: Series([1, 3, 4]).quantile(0.5, interpolation="lower")
Out[2]: 3.0

In [3]: import pandas

In [4]: pandas.Series([1, 3, 4]).quantile(0.5, interpolation="lower")
Out[4]: 3

In [5]: Series([1, 3, 4]).median()
Out[5]: 3.0

Ideally, it would be great for odd number of values that quantile(0.5) and median respect the original type and not always cast to float.

Describe the solution you'd like
When possible, downcast to the original type for quantile and median

Describe alternatives you've considered
N/A

Additional context
Add any other context, code examples, or references to existing implementations about the feature request here.