Update how we send skills to the skills API

[jmgasper]

@suppermancool - The API has changed from the work-skills endpoint. We will now be sending skills like this, when a user modifies the selected skills for a challenge:

POST https://api.topcoder-dev.com/v5/standardized-skills/challenge-skills/{challenge ID}

Body:

{
    "skillIds": [
        "4458454c-9a97-4332-a545-6546e240dab6",
        "63bb7cfc-b0d4-4584-820a-18c503b4b0fe",
        "fcbac194-35ab-4a31-aa7c-a2867fff9c4b"
    ]
}