[Documentation]: MPPI and MPC path tracking

[mohitk3000]

Description
Currently, the MPC and MPPI path tracking are integrated in the code base.
I would like to propose documentation for these controllers that explains the maths, code, optimization process, and a comparison of how MPC and MPPI work.

Tasks:

• MPPI doc

• MPC doc

[ShisatoYano]

@mohitk3000 Sounds great suggestion! I’m looking forward to reviewing your PR!!