Make rotate function compatible with cupy

[GenevieveBuckley]

The dask_image.ndinterp.rotate function currently supports numpy backed dask arrays, but not cupy GPU arrays. It would be nice to extend the functionality to add GPU support.

Suggested approach:
One way to approach this could be to:

1. Try and split out the sub-section of the rotate function that makes the rotation matrix, and put this into a separate helper function (i.e. group all the numpy specific lines of code together, while keeping the function as small as possible to reduce code duplication later).
2. Make a second version of the helper function using cupy/cupyx functions replacing all the lines that call numpy directly.
3. Then we could use the same dispatch mechanism as we do with the other modules (see the dask_image/dispatch folder) to register our new numpy and cupy versions.
4. Add a test for the new functionality
5. Update the coverage.rst table, adding a tick mark to indicate this function now has GPU support