Update ROCm base docker images to focal (ubuntu20.04) (attempt #2) (#81031)
Re-attempting after original PR https://github.com/pytorch/pytorch/pull/79596 was reverted due to causing ROCm build failures
Pull Request resolved: https://github.com/pytorch/pytorch/pull/81031
Approved by: https://github.com/jeffdaily, https://github.com/malfet
