Tabulator: Separate aggregators for different columns blocked by type hint

[AxZolotl]

Software Version Info

panel 1.4.5 

Description of expected behavior and the observed behavior

• 'If separate aggregators for different columns are required the dictionary may be nested as {index_name: {column_name: aggregator}}'
• Aggregators parameter in class DataTabulator accepts only Dict(String, String)

Complete, minimal, self-contained example code that reproduces the issue

pn.widgets.Tabulator(
            value = value, 
            hierarchical = True, 
            aggregators = {index_name: {column_name: aggregator}}

Stack traceback and/or browser JavaScript console output

ValueError: failed to validate DataTabulator(id=id, ...).aggregators: expected a dict of type Dict(String, String), got a dict with invalid values for keys: index_name