ENH: Preserve attrs when converting to pandas dataframe

[snowman2]

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

import xarray

xds = xarray.DataArray([1], name="a", dims="a", attrs={"long_name": "Description about data"})

xds.attrs

Output:

{'long_name': 'Description about data'}

xds.to_dataframe().a.attrs

Output:

{}

Describe the solution you'd like
It would be nice if the attributes of the DataArray were preserved in each pandas.Series and the attributes of each Dataset were preserved on the pandas.Dataframe

Additional context

Things to be wary about is that it the pandas documentation says the attrs is experimental.