KeyValueTags are 1:n in Steamworks but 1:1 in Facepunch

[Lothsahn]

Describe the bug
KeyValue tags are documented (and function in steamworks) as 1:n tags:
https://partner.steamgames.com/doc/api/ISteamUGC#AddItemKeyValueTag

Multiple tags, and even duplicates of the same tag, are allowed.

In Facepunch, 1:n is allowed when writing tags. However, when reading tags off an Item, they are stored in a Dictionary of <string, string>. Duplicate values for a key collide and disappear. The current definition in UgcItem.cs is:
public Dictionary<string,string> KeyValueTags { get; internal set; }

The proper structure is:
public Dictionary<string,List> KeyValueTags { get; internal set; }

To Reproduce

1. Create multiple values for the same key using KeyValue Tags. For instance:
   var result = await Steamworks.Ugc.Editor.NewCommunityFile
   .WithTitle($"Test")
   .AddKeyValueTag("testkey", "testvalue1")
   .AddKeyValueTag("testkey", "testvalue2")

2. Read the values back with a UGCItem and notice that only one of the two values is read.

Calling Code

    private static async Task<Item> GetFirstItemForQuery(Query query)
    {
      List<Item> itemsForQuery = await GetItemsForQuery(query);
      if (itemsForQuery.Count > 0)
      {
        return itemsForQuery[0];
      }
      
      return new Item(0);
    }
    private static async Task<List<Item>> GetItemsForQuery(Query query)
    {
      List<Item> itemList = new();
      ResultPage? page;
      int x = 1;
      do
      {
        page = await query.GetPageAsync(x);
        x++;
        if (page.HasValue)
        {
          Debug.Log($"Got page back... {page.Value.TotalCount} item");
          foreach (var entry in page.Value.Entries)
          {
            Debug.Log($"Found item with Title:{entry.Title} and ID:{entry.Id}");
            itemList.Add(entry);
          }
        }
      } while (page.HasValue && page.Value.ResultCount > 0);

      if (itemList.Count == 0)
      {
        Debug.Log($"Did not find any results for query.");
      }

      return itemList;
    }

query = Query.All
          .WithKeyValueTags(true);
        
        Item item = await GetFirstItemForQuery(query);
        Debug.Log(item.KeyValueTags["testkey"]);

Expected behavior
I expect to see both keys in the output

Desktop (please complete the following information):

• OS: Windows
• Unity: 2022.3.f51

Additional context
Patch incoming.

[Lothsahn]

PR available:
#732