Create skeleton of get/delete model endpoints

[leoll2]

Create a skeleton for the following endpoints:

• GET /api/projects/<id>/models
• GET /api/projects/<id>/models/<model_id>
• GET /api/projects/<id>/models/<model_id>/labels
• DELETE /api/projects/<id>/models/<model_id>

Model response:

{
  "id": "76e07d18-196e-4e33-bf98-ac1d35dca4cb",
  "architecture": "Object_Detection_YOLOX_X",
  "parent_revision": "06091f82-5506-41b9-b97f-c761380df870",
  "training_info": {
    "status": "in_progress",
    "start_time": "2021-06-29T16:24:30.928000+00:00",
    "end_time": "2021-06-29T16:24:30.928000+00:00",
    "dataset_revision_id": "3c6c6d38-1cd8-4458-b759-b9880c048b78",
    "label_schema_revision": {...},
    "configuration": {...},
  }
  "files_deleted": false,
}