Add epsilon argument to Adagrad optimizer (#24980)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/24980
We'll need this internally, so just updating the open source version. the other optimizers have this argument anyways.
Test Plan: Imported from OSS
Differential Revision: D16945279
Pulled By: li-roy
fbshipit-source-id: 0b8cc86f15387cd65660747899d3d7dd870cff27
