Moving extension installation from post install to setup.py under project root folder

[tocean]

What would you like to be added: Moving extension installation from post install to setup.py under project root folder.

Why is this needed: Extensions are part of MS-AMP and should be installed with MS-AMP package.

Without this feature, how does current msamp work： MS-AMP use make postinstall to install pytorch extensions such as distop and optim.

Components that may involve changes: msamp.operators.dist_op and msamp.optim

Brief description of your proposal if any: