Allow the creation of "entity groups" for NerPipeline #3548 (#3957)
* Add index to be returned by NerPipeline to allow for the creation of
* Add entity groups
* Convert entity list to dict
* Add entity to entity_group_disagg atfter updating entity gorups
* Change 'group' parameter to 'grouped_entities'
* Add unit tests for grouped NER pipeline case
* Correct variable name typo for NER_FINETUNED_MODELS
* Sync grouped tests to recent test updates