Add possibility to serialize objects as JSON with indentation

[henrikfroehling]

The output of

ITraktShow show = ...; // Show: The Last of Us
string json = await TraktSerializationService.SerializeAsync(show);
Console.WriteLine(json);

looks like this:

{"title":"The Last of Us","year":2023,"ids":{"trakt":158947,"slug":"the-last-of-us","tvdb":392256,"imdb":"tt3581920","tmdb":100088}}

TraktSerializationService.SerializeAsync() should get an optional boolean parameter indentation, which indents the JSON output like this:

{
    "title":"The Last of Us",
    "year":2023,
    "ids":
    {
        "trakt":158947,
        "slug":"the-last-of-us",
        "tvdb":392256,
        "imdb":"tt3581920",
        "tmdb":100088
    }
}

API Change:

namespace TraktNet.Services
{
+    public static Task<string> SerializeAsync(ITraktAuthorization authorization, bool indentation, CancellationToken cancellationToken = default);

+    public static Task<string> SerializeAsync<TObjectType>(TObjectType obj, bool indentation, CancellationToken cancellationToken = default);

+    public static Task<string> SerializeCollectionAsync<TObjectType>(IEnumerable<TObjectType> objects, bool indentation, CancellationToken cancellationToken = default);
}