Add indexes to grouped entity NER pipeline
# 🚀 Feature request

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     Please provide a link to the paper and code in case they exist. -->
**There should be indexes in the output of the grouped entity NER pipeline**

The standard NER pipeline from transformers outputs entities that contain the word, score, entity type, and index. The following snippet demonstrates the normal behavior of the NER pipeline with the default `grouped_entities=False` option.

```python
from transformers import pipeline
nlp_without_grouping = pipeline("ner")
sequence = "Hugging Face Inc. is a company based in New York City."
print(nlp_without_grouping(sequence))

[
    {'word': 'Hu', 'score': 0.9992662668228149, 'entity': 'I-ORG', 'index': 1},
    {'word': '##gging', 'score': 0.9808881878852844, 'entity': 'I-ORG', 'index': 2},
    {'word': 'Face', 'score': 0.9953625202178955, 'entity': 'I-ORG', 'index': 3},
    {'word': 'Inc', 'score': 0.9993382096290588, 'entity': 'I-ORG', 'index': 4},
    {'word': 'New', 'score': 0.9990268349647522, 'entity': 'I-LOC', 'index': 11},
    {'word': 'York', 'score': 0.9988483190536499, 'entity': 'I-LOC', 'index': 12},
    {'word': 'City', 'score': 0.9991773366928101, 'entity': 'I-LOC', 'index': 13}
]

```

However, the NER pipeline with `grouped_entities=True` outputs only word, score, and entity type. Here's the code snippet and output. There's also the problem of 'New York City' being duplicated, but I will address that in a new issue.
```python
from transformers import pipeline
nlp_with_grouping = pipeline("ner", grouped_entities=True) 
sequence = "Hugging Face Inc. is a company based in New York City."
print(nlp_with_grouping(sequence))

[
    {'entity_group': 'I-ORG', 'score': 0.9937137961387634, 'word': 'Hugging Face Inc'},
    {'entity_group': 'I-LOC', 'score': 0.9990174969037374, 'word': 'New York City'},
    {'entity_group': 'I-LOC', 'score': 0.9990174969037374, 'word': 'New York City'}
]
```

I believe that the grouped entities returned should also include the tokens of the entities. Sample output would look as such
```python
[
    {'entity_group': 'I-ORG', 'score': 0.9930560886859894, 'word': 'Hugging Face Inc', 'indexes': [1, 2, 3, 4]},
    {'entity_group': 'I-LOC', 'score': 0.998809814453125, 'word': 'New York City', 'indexes': [11, 12, 13]},
    {'entity_group': 'I-LOC', 'score': 0.998809814453125, 'word': 'New York City', 'indexes': [11, 12, 13]}
]
```

## Motivation

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     related to a problem? e.g., I'm always frustrated when [...]. If this is related
     to another GitHub issue, please link here too. -->

**Any application that requires users to locate grouped named entities would require some sort of index.** This feature is present in the standard NER pipeline and should also exist in the grouped entity NER pipeline as well. 

In my case, I am trying to append the type to the text right after the named entity ("Apple" would become "Apple \<I-ORG\>") so I need to be able to locate the named entity within my phrase.

## Your contribution

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     Make sure to read the CONTRIBUTING.MD readme:
     https://github.com/huggingface/transformers/blob/master/CONTRIBUTING.md -->

I have been able to fix this by adding two lines to `group_sub_entities` function https://github.com/huggingface/transformers/blob/7fad617dc1fc681a7f5da5e0172c8b83f4bf0024/src/transformers/pipelines.py#L1042
```python
    def group_sub_entities(self, entities: List[dict]) -> dict:
        """
        Returns grouped sub entities
        """
        # Get the first entity in the entity group
        entity = entities[0]["entity"]
        scores = np.mean([entity["score"] for entity in entities])
        tokens = [entity["word"] for entity in entities]
        indexes = [entity["index"] for entity in entities]    # my added line

        entity_group = {
            "entity_group": entity,
            "score": np.mean(scores),
            "word": self.tokenizer.convert_tokens_to_string(tokens),
            "indexes": indexes    # my added line
        }
        return entity_group
```
This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.
<|||||>I am facing the same issue, Does this issue got fixed<|||||>This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.
<|||||>Fixed by https://github.com/huggingface/transformers/pull/8781