split do_extarctor_overlap to correctly handle overllappine entities

[EPedrotti]

Proposed changes:

• split determine_token_labels in two functions, determin_token_labels and determine_true_token_labels. This should handle correctly overlapping entities, and throw an exception only if overlapping entities are found and a extractor that does not support them is used.

Status (please check what you already did):

• made PR ready for code review
• added some tests for the functionality
• updated the documentation
• updated the changelog

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[akelad]

ok actually i think we've ended up complicating this way too much, simply changing the do_extractors_support_overlap to:

def do_extractors_support_overlap(extractors):
    """Checks if extractors support overlapping entities
    """
    if extractors is None:
        return False
    return CRFEntityExtractor.name not in extractors

will solve all our problems i believe. So if you could close this PR and open a new one with that change, that'd be great. I think writing some tests for this makes sense as well, so some examples where there's no extractor field/crf in there and the entities are overlapping, and some for when the extractors are ner_spacy etc.

[tmbo]

@EPedrotti can we close this in favor of #1760 ?