Migrate qiskit_sphinx_theme to the new theme

[zlatko-minev]

Please be as descriptive as possible, including: what is expected, why is this feature needed, what is the objective, etc.

What is the feature being requested?

In qiskit-sphinx-theme 1.14, we replaced the old qiskit_sphinx_theme based on Pytorch with the new qiskit-ecosystem theme based on Furo. The old theme was removed in qiskit-sphinx-theme 2.0.

See Migrate from old Pytorch theme to new theme for migration instructions.

See https://github.com/Qiskit/qiskit_sphinx_theme/blob/1.16/README.md#migrate-from-old-pytorch-theme-to-new-theme

What are use cases for this feature?

[zlatko-minev]

To solve in #1002