CE-1783: Separate IOC instances from Operation to a new endpoint

Fetching IOC instances of an operation has been moved to a new endpoint:

[GET] /api/v1/operation/{operation_id}/instances

It response schema is:

{
    "operation_id": 1,
    "instances": [{
            "instance_name": "name-1",
            "instance_git_url": "url1",
            "id": 1
        },
        {
            "instance_name": "name-2",
            "instance_git_url": "url2",
            "id": 2
        },
        {
            "instance_name": "name-3",
            "instance_git_url": "url3",
            "id": 3
        }
    ]
}