feat: Add moving average plot

[Gerhardsa0]

Is your feature request related to a problem?

The user should be able to see the moving average in context with the time series.

Desired solution

The user should just call something like this: ts.plot_movingaverage()
When implementing this, the pandas df.roll-function could be pretty useful.

https://pandas.pydata.org/docs/reference/api/pandas.DataFrame.rolling.html

[Gerhardsa0]

@lars-reimann
for the implementation I could use this function: https://docs.pola.rs/api/python/stable/reference/expressions/api/polars.Expr.rolling_mean.html

But it's considered unstable, so should I use this function, or write an own rolling average?

[lars-reimann]

Use the polars version. If they change it, we change the implementation of our wrapper.

[Gerhardsa0]

Should there also be an moving average function for a Column, which calculates the moving average and returns it as a column.
The same goes for windows.

[lars-reimann]

Maybe later, you don't have to worry about that.