matchms similarity: Add MS2DeepScore metric

[hechth]

Models could again be passed as a parameter for the tool so that the model can be trained offline and then passed to the matching module.

• Similarity metric
• model training

AFAIK the models can be read using the function here as a keras model.

The model could therefore be trained offline in the first stage and then later we could implement the training step as a separate tool.