Add stl, stp (STEP) files for SRA Board, LSA and MPU

[Dhairya Shah]

Uses-

1. Essential and easy to export in other CAD software (Solidworks, Coppelia, FreeCAD, etc)
2. Useful for use in simulation

Kindly add these files and update them here.

• Replace the old files.
• This should be done for sra_board, LSA, and MPU in respective directories
• @Aniruddha1261 kindly make the required changes and update your PR

[Omkar Bhilare]

solved here #7