[NLP] Add support for the pass_through task

[davidkyle]

The pass_through task returns the models output directly without any post-processing of the results. pass_through is typically used for debugging.

This change allows models to be loaded into Elasticsearch with the pass_through task

An example invocation of the eland_import_hub_model script with pass_through is:

eland_import_hub_model \
      --url XXX \
      -u XXX -p XXXX \
      --hub-model-id "sentence-transformers/msmarco-MiniLM-L-12-v3" \
      --task-type pass_through 

[droberts195]

LGTM