Add preconditioned CGLS using the new preconditioner class

[MargaretDuff]

Description

I think potentially, we give the option of applying a pre-conditioner to the residual $r$ after these lines in the CGLS update step: https://github.com/TomographicImaging/CIL/blob/8d111a37cec72756d4b8d80f526ff22333019037/Wrappers/Python/cil/optimisation/algorithms/CGLS.py#L101-L103

Applying a pre-conditioner of $M^{-1}r$ should be equivalent to the preconditioned algorithm on Wikipedia https://en.wikipedia.org/wiki/Conjugate_gradient_method (I think - Need to check with someone else! )