Introduce methods on new service to have alternative to obsoleted methods

[bergmania]

Description

Fixes #17202

Introduce two methods on the IEntityTypeContainerService<T>:

• Task<IEnumerable> GetAsync(string name, int level);
• Task<IEnumerable> GetAllAsync();

Test

You can test it out by creating some data type folders and request them, e.g. just in a view like this

@using Umbraco.Cms.Core.Services
@inherits Umbraco.Cms.Web.Common.Views.UmbracoViewPage
@inject IDataTypeContainerService DataTypeContainerService;
@{
	Layout = null;

    var x = await DataTypeContainerService.GetAllAsync(); // returns all three
    var y = await DataTypeContainerService.GetAsync("Subfolder", 1); // Returns only the subfolder in the root
    var z = await DataTypeContainerService.GetAsync("Subfolder", 2); // Returns only the subfolder under folder
}

In this example I made the following folders

• Folder
  • Subfolder
• Subfolder