[special] alias for mvlgamma (#61633)
Summary:
Reference: https://github.com/pytorch/pytorch/issues/50345
Have added `out` variant for consistency.
TODO:
* [x] Check docs https://docs-preview.pytorch.org/61633/special.html#torch.special.multigammaln
Pull Request resolved: https://github.com/pytorch/pytorch/pull/61633
Reviewed By: albanD
Differential Revision: D29815514
Pulled By: mruberry
fbshipit-source-id: 003c7b6a5938ecc7a96727310e8a39da0b3d7aca
