RGD optimization method for quantum state tomography

[HuberyMing]

Checklist:

• [ ] Reviewers confirm new code works as expected.
• [ ] Tests are passing.
• [ ] Coverage does not decrease.
• [ ] Documentation is updated.

To include the optimization method of Riemannian Gradient Descent (RGD) algorithm to do the tomography problem. The implementation follows from the arXiv:2210.04717, which was published in Phys. Rev. Lett. 132, 240804