Implement a first version of the clear indexes

[irevoire]

Prototype prototype-clear-all-indexes-0

• Provide a new DELETE /indexes route to delete all indexes
• In the task queue:
  • Reuse the indexDeletion type but set the indexUid to null => Should we create a new type for this task?
  • What should be the details?

  {
    "uid": 243,
    "indexUid": null,
    "status": "succeeded",
    "type": "indexDeletion",
    "canceledBy": null,
    "details": {
      "deletedDocuments": null
    },
    "error": null,
    "duration": "PT0.008237S",
    "enqueuedAt": "2023-05-09T08:54:19.507495Z",
    "startedAt": "2023-05-09T08:54:19.511285Z",
    "finishedAt": "2023-05-09T08:54:19.519522Z"
  }

I made this PR to explore the subject, but feedback and bug reports are greatly appreciated to help us shape a solution.