Add the L-curve solver from `opflow.NaturalGradient`

[Cryoris]

What should we add?

The L-curve solver implemented in qiskit.opflow.NaturalGradient is a powerful solver for ill-conditioned linear systems. It determines the required regularization by trading off noise in the solution and introduced bias and is an important subroutine in variational time evolution, natural gradient descent or 2nd order gradient descent.

It would be great to have a submodule solvers or linear_systems next to qiskit_algorithms.optimizers where we can add this function.