GitLab

* Add nn.layer: softmax, attention, transformer
Signed-off-by: Shijie Wang <jaywan@nvidia.com>

* code refactor
Signed-off-by: Shijie Wang <jaywan@nvidia.com>

* code refactor
Signed-off-by: Shijie Wang <jaywan@nvidia.com>

* update docs and set dropout=0.1
Signed-off-by: Shijie Wang <jaywan@nvidia.com>

* Update transformer_engine/paddle/layer/attention.py
Signed-off-by: Kirthi Shankar Sivamani <ksivamani@nvidia.com>

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Signed-off-by: Shijie Wang <jaywan@nvidia.com>
Signed-off-by: Kirthi Shankar Sivamani <ksivamani@nvidia.com>
Co-authored-by: Kirthi Shankar Sivamani <ksivamani@nvidia.com>