[distributed][docs] Delete distributed optimimzer section from RPC and add reference to namespace docs page (#68068)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/68068
cc pietern mrshenli pritamdamania87 zhaojuanmao satgera rohan-varma gqchen aazzolini osalpekar jiayisuse SciPioneer H-Huang
Test Plan: Imported from OSS
Reviewed By: pritamdamania87
Differential Revision: D32286554
Pulled By: jamesr66a
fbshipit-source-id: a43fe1f0cfa74721f467b128f2e878bd02f32546
