[ENH] Forecasting first version

[TonyBagnall]

Describe the feature or idea you want to propose

Relaunch of forecasting as described in AEP 8
aeon-toolkit/aeon-admin#14

The whole principle is to start simple, get core functionality, then expand.

Describe your proposed solution

see #2244 and #2248

• Base forecaster class as BaseSeriesEstimator
• Regression forecaster containing windowing and an aeon/sklearn forecasters
• Basic ETS forecaster with numba
• First notebook describing basic use cases