[BUG] IntervalColumn loosing type metadata when Index.union operation is performed

[galipremsagar]

Describe the bug
When a union operation is performed on IntervalIndex, type metadata are being lost.

Steps/Code to reproduce bug

In [1]: import cudf

In [2]: import pandas as pd

In [3]: idx = pd.IntervalIndex.from_tuples([(0, 2), (0, 2),(2, 4)])

In [4]: gidx = cudf.from_pandas(idx)

In [5]: gidx
Out[5]: IntervalIndex([(0, 2], (0, 2], (2, 4]], dtype='interval[int64, right]')

In [7]: ngidx = cudf.from_pandas(pd.IntervalIndex.from_tuples([ (0, 2),(2, 4)]))

In [8]: gidx.union(ngidx)
Out[8]: IntervalIndex([{'0': 0, '1': 2}, {'0': 0, '1': 2}, {'0': 2, '1': 4}], dtype='struct')

Expected behavior

In [9]: gidx.to_pandas().union(ngidx.to_pandas())
Out[9]: IntervalIndex([(0, 2], (0, 2], (2, 4]], dtype='interval[int64, right]')

Environment overview (please complete the following information)

• Environment location: [Bare-metal]
• Method of cuDF install: [from source]