Add cupyx.profiler to python module API list

[arkdong]

I've add cupyx.profiler to python module API list via adding .. module:: cupyx.profiler in the file est.rst, regarding to issue #6018

Initially just adding the line of code threw an exception that no module named cupyx.profiler, but after trying different implementation I found that when moving the hole code piece to the bottom of the file above .. _kernel_param_opt: will work.

I've tested using sphinx-build -b html . _build to build the html page, and opened with xdg-open _build/py-modindex.html. The hyperlink of profiler work as expected, and the code below for cupyx.optimizing will not be affected. The only thing that changed on the page for cupy-specific fuctions, is the order of each section.