[ENH] Support for probabilistic forecasting of global forecasters

[Xinyu-Wu-0000]

Related [ENH] Support Global Time Series Forecasting #4651

Currently the global forecasting interface can only perform point forecast, we need to add probabilistic forecast functions to it.

The first step would be adding quantile forecast for pytorch-forecasting interface: [ENH] Adapter to pytorch-forecasting #4923.

In the future, with more models that support different probabilistic forecast methods, we can add other probabilistic forecast functions.