Add SoftEmbedding projection option for coninuous_features of SequentialTabularFeatures

[sararb]

• The project_continuous_features only supports MLP projection.
• We should include SoftEmbedding projection as well:

  Transformers4Rec/transformers4rec/torch/features/embedding.py

  Line 296 in fd904fd

  class SoftEmbeddingFeatures(EmbeddingFeatures):