Index issues with render.table and render.data_frame

I ran into a bit of unexpected behaviour rendering data tables. When calculating group-wise statistics in pandas we don't include the grouping column by default in the rendered table unless the user sets index=True. There are two issues with this:

1. The default for printing pandas tables includes the index, so we should follow that pattern
2. render.data_frame doesn't seem to have support for printing indexes, or at least follows a different API pattern

from shiny import App, render, ui, reactive
import pandas

import pandas as pd

data = {
    "group": ["A", "A", "B", "B", "A", "B", "A", "B"],
    "value1": [10, 20, 30, 40, 50, 60, 70, 80],
    "value2": [5, 15, 25, 35, 45, 55, 65, 75],
}

df = pd.DataFrame(data)

means_by_group = (
    df.set_index("group")
    .groupby(level="group")
    .agg({"value1": "mean", "value2": "mean"})
)
app_ui = ui.page_fluid(ui.output_table("table"), ui.output_data_frame("df"))


def server(input, output, session):
    @output
    @render.table(index=True)
    def table():
        return means_by_group

    @output
    @render.data_frame()
    def df():
        return means_by_group


app = App(app_ui, server)

Start by reproducing the grouped pandas example and read the render.table(index=True) and render.data_frame entry points to compare their index APIs and defaults. Done means both renderers consistently expose the grouping/index column, with the intended default matching pandas table output.