[FEA] Support groupby collect agg on struct columns

**Is your feature request related to a problem? Please describe.**
Ability to create a list of struct columns using the `collect` agg via groupby

**Describe the solution you'd like**
```python
df = cudf.DataFrame(
{
'a':['aa','aa','cc'],
'd':[{"b": '1', "c": "one"}, {"b": '2', "c": "two"}, {"b": '3', "c": "one"}]
}
)

df.groupby('a').collect()

d
a
aa [{'b': '1', 'c': 'one'}, {'b': '2', 'c': 'two'}]
cc [{'b': '3', 'c': 'one'}]
```

**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.