Add conjugate gradient method algorithm (#2486)

* Initial commit of the conjugate gradient method
* Update linear_algebra/src/conjugate_gradient.py
* Added documentation links, changed variable names to lower case and more descriptive naming, added check for symmetry in _is_matrix_spd
* Made changes to some variable naming to be more clear
* Update conjugate_gradient.py

Co-authored-by: Zeyad Zaky <zeyadzaky@Zeyads-MacBook-Pro.local>
Co-authored-by: Christian Clauss <cclauss@me.com>
Co-authored-by: Dhruv Manilawala <dhruvmanila@gmail.com>