[🕹️]Added the notebook for currency exchange rate prediction

[Manish-k723]

1. Why?:

To contribute an enhanced feature to OpenBB that improves forex prediction using various time series models and to showcase it in a notebook format for ease of understanding and usage.

2. What?:

Implemented a notebook demonstrating the usage of ARIMA, SARIMAX, Exponential Smoothing, and LSTM models for predicting forex prices based on historical data.

3. Impact:

• Enables users to better forecast currency exchange rates using multiple models.
• Improves model selection flexibility for time series analysis.

4. Testing Done:

Validated with historical forex data from OpenBB, comparing the actual prices to the predicted ones across all models used.

5. Reviewer Notes:

I would appreciate any constructive feedback on this PR. If there are any areas for improvement, please share your insights by raising the issues. This will help in refining the changes rather than closing the PR prematurely.

closes #6716