Feature Request: Ability to overlay a candle chart over another (share axes)

Thank you for your work on updating mplfinance!

Using the deprecated mpl-finance, I was able to put 2 `candlestick_ohlc()` charts on top of each other (overlaid, sharing the same axes), and a table below the chart, all within a single figure that could be saved.

Now, I can use `returnfig=True` to export the figure and axes, but not sure how to actually use those later. `ax` is not a valid kwarg in `plot()`, as it was in `candlestick_ohlc()`. And not sure how to draw the chart inside a parent figure. Should `fig` be a kwarg for `plot()`?

Thank you.

Start by reading the current plot() and returnfig behavior, then compare it with the deprecated candlestick_ohlc() use of ax. Clarify how a parent figure and shared axes should be supplied, including the requested table below the chart. Done means two candle charts can be overlaid in one saveable figure.

Written by the indexing model from the issue text.