Add Native AOT compatibility

[mcdis]

var client = new GitLabClient("https://git.xxx.yy", "XXX");

var groupQueryAllAvailable = new GroupQuery
{
  AllAvailable = true,
};

foreach (var group in client.Groups.GetAsync(groupQueryAllAvailable))
  Console.WriteLine(group.Name);

csproj

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net8.0</TargetFramework>
    <PublishAot>true</PublishAot>
  </PropertyGroup>
  <ItemGroup>
    <PackageReference Include="NGitLab" Version="6.50.2" />
  </ItemGroup>
</Project>

Error occurs:

System.InvalidOperationException: 
'Reflection-based serialization has been disabled for this application. 
Either use the source generator APIs or explicitly 
configure the 'JsonSerializerOptions.TypeInfoResolver' property.'

Stack-trace:

   at System.Text.Json.ThrowHelper.ThrowInvalidOperationException_JsonSerializerIsReflectionDisabled()
   at System.Text.Json.JsonSerializerOptions.ConfigureForJsonSerializer()
   at System.Text.Json.JsonSerializer.GetTypeInfo(JsonSerializerOptions options, Type inputType)
   at System.Text.Json.JsonSerializer.GetTypeInfo[T](JsonSerializerOptions options)
   at System.Text.Json.JsonSerializer.Deserialize[TValue](String json, JsonSerializerOptions options)
   at NGitLab.Impl.Json.Serializer.Deserialize[T](String json) <-- HERE
   at NGitLab.Impl.HttpRequestor.Enumerable`1.<GetEnumerator>d__5.MoveNext() <-- HERE
   at Program.<Main>$(String[] args) in D:\imba.sandbox\gitlab-roles\gitlab-roles\Program.cs:line 12

[jairbubbles]

Hi @mcdis, indeed it would be great to have NGitLab ready for AOT.

I created a draft PR regarding the serialisation : #687

But there are other method calls which are problematic.