add tags into chunks

[oalam]

• chunk_tags field (array to be specified with gateway team)

[MiniPlayer]

The tags should be added in a separate Collection than chunks.
We called for exemple this collection "annotations".
Each particular event would be indexed in this collection in the following format :

  {
    "time": 1581075145188,
    "timeEnd": 1581075145188,
    "text": "drop of 3 detected",
    "tags": [
      "metric_1", "drop"
    ]
  }

All fields are required except for timeEnd when the event is momentaneous.