/// <summary>
/// Adds the ability for this graphql server to raise subscription events as well
/// as creates a subscription server that can accept connected clients and respond to subscription events. This extension will attempt to inject subscription related
/// middleware into the primary query excution pipeline and replace it. Call this method before injecting or
/// adding your own query execution middleware items.
/// </summary>
/// <typeparam name="TSchema">The type of the schema being built.</typeparam>
/// <param name="schemaBuilder">The schema builder.</param>
/// <param name="options">An action function to configure the subscription options.</param>
/// <returns>ISchemaBuilder<TSchema>.</returns>
public static ISchemaBuilder <TSchema> AddSubscriptions <TSchema>(
this ISchemaBuilder <TSchema> schemaBuilder,
Action <SubscriptionServerOptions <TSchema> > options = null)
where TSchema : class, ISchema
{
// publsihing is registered AFTER the subscription server
// because subscription server rebuilds the query execution pipeline
// then publishing adds one additional middleware component
return(schemaBuilder
.AddSubscriptionServer(options)
.AddSubscriptionPublishing());
}