Gaussian process

[Lyuchenyi]

This PR introduces the GaussianProcess folder in the Stone Soup framework, which includes two Gaussian Process implementations (GP) implementations. Additionally, it contains a comparison between GP and Kalman Filter (KF) and an implementation of GP with multi-dimensional output support.

Changes:
Added a new GaussianProcess/ directory, which includes:

• First GP implementation (based on Fusion conference paper).
• Second GP implementation (located in NewGPproject/, relies on "GaussianProcessPredictor" and "gaussianprocess" to achieve the GP).
• Comparison experiments between GP and Kalman Filter (analyzing GP’s performance in target tracking tasks).
• Multi-dimensional output GP implementation (an extended GP method supporting high-dimensional state modelling).