add conv2d module (#4764)

* add conv2d module

* support bias

* add conv2d test

* update conv2d test

* return nullptr instead of LOG(FATAL) when arg is not found

* format

* format & update conv2d test

* update test

* add reset_parameters for conv2d

* fix a bug

Co-authored-by: daquexian <daquexian566@gmail.com>
Co-authored-by: oneflow-ci-bot <69100618+oneflow-ci-bot@users.noreply.github.com>