feat: add GitHub release API client and response DTOs

Program.cs

@@ -11,5 +11,14 @@ var repositoryConfig = await RepoConfigLoader.LoadConfigAsync(
     config.RepositoryConfigFilePath);
 builder.Services.AddSingleton(repositoryConfig);
 
+builder.Services.AddSingleton<GithubService>();
+
 var app = builder.Build();
+
+using var scope = app.Services.CreateScope();
+
+await scope.ServiceProvider
+    .GetRequiredService<GithubService>()
+    .FetchRepoReleasesAsync("SagerNet","sing-box");
+
 await app.RunAsync();