DOC: move from ``sphinx-panels`` to ``sphinx-design``

[phofl]

Pandas version checks

• I have checked that the issue still exists on the latest versions of the docs on main here

Location of the documentation

sphinx-panels is no longer maintained and restricts our sphinx version. The maintainers recommend using sphinx-design.

https://github.com/executablebooks/sphinx-panels

We should switch I guess.

Documentation problem

sphinx panels no longer maintained

Suggested fix for documentation

move over