Sort transforms alphabetically in docs

[brudfors]

The transforms documentation would be easier to navigate if the transforms were sorted alphabetically. It would, for example, then be easier to see what transforms have a random implementation (prefixed Rand*), compared to currently:

[wyli]

thanks for the suggestion, adding an indexing page
https://docs.monai.io/en/latest/transforms_idx.html

so that the transform classes are generated automatically and listed by names

https://github.com/Project-MONAI/MONAI/blob/dev/docs/source/transforms_idx.rst

example: https://docs.monai.io/en/latest/_gen/monai.transforms.croppad.array.html#module-monai.transforms.croppad.array