Add withSetProviders method

[ghostwriter]

This patch resolves rectorphp/rector#8720 (comment), via the following changes:

• Add a new withSetProviders method, to add set provider class names to the setProviders array, including validation to ensure they implement the SetProviderInterface.

• Modified the __invoke method to handle both setGroups and setProviders when creating a SetManager instance.

<?php

declare(strict_types=1);

use Vendor\Package\RectorSetProvider;
use Vendor\Package\ComposerSetProvider;
use Rector\Config\RectorConfig;

return RectorConfig::configure()
           ->withSetProviders(
               RectorSetProvider::class,
               ComposerSetProvider::class
           );

Note: I haven't added tests, but this can serve as a starting point, if you like the idea.

[TomasVotruba]

Thank you, looks good to me 👍