docs: def get_first_date_of_index(elastic_url, index):
      """Get the first/min date present in the index"""
      es = Elasticsearch(elastic_url)
      search = Search(using=es, index=index)
      agg = A("min", field="grimoire_creation_date")
      search.aggs.bucket("1", agg)
      search = search.extra(size=0)
      response = search.execute()
      start_date = response.to_dict()['aggregations']['1']['value_as_string'][:10]
      return start_date