Replace string[] DeliveryChannels with DeliveryChannel[] DeliveryChannels

[tomcrane]

Replace the string[] DeliveryChannels property on the Hydra Image API class in the DLCS with DeliveryChannel[] DeliveryChannels as per the new documentation. Nothing will be calling this any more. All old calls still get routed to OldDeliveryChannels via .wcDeliveryChannels on hydra JSON.

Leave that property intact on the Hydra class, but ALL use of it within the DLCS is now for removal, as the new behaviour is implemented. We'll come back to deal with this property in #714

This is a very small task but is the prep for the full implementation work.

We also, during the full implementation, need to remove all usage of ImageOptimisationPolicy and ThumbnailPolicy.

We don't necessarily have to have a specific task to rip it all out before introducing the new DeliveryChannels. Better to replace bit by bit, so we can see what the old code is doing in places as we implement the new. But the old code will never more be executed, and by the end of the work, the fields and the code that uses them must be gone.

[tomcrane]

Acceptance criteria

• There is a DeliveryChannel Hydra class
• For this ticket, posting new DeliveryChannels is a no-op (impl happens in other tickets)
• The DLCS model class Asset stays the same, but we translate from hydra wcDeliveryChannels to Asset.DeliveryChannels, e.g., at

  protagonist/src/protagonist/API/Converters/AssetConverter.cs

  Line 275 in 7672a78

  asset.DeliveryChannels = hydraImage.DeliveryChannels.OrderBy(dc => dc).Select(dc => dc.ToLower()).ToArray();

• wcDeliveryChannels becomes string[] and is used directly

[tomcrane]

    [JsonProperty(Order = 141, PropertyName = "wcDeliveryChannels")]
    public string[]? WcDeliveryChannels { get; set; } // requires refactor first

    [JsonProperty(Order = 140, PropertyName = "deliveryChannels")]
    public DeliveryChannel[]? DeliveryChannels { get; set; }