add OpenRouter

[rrr63]

Adding OpenRouter

Can be called with :

use Doppar\AI\Agent;
use Doppar\AI\AgentFactory\Agent\OpenRouter;

$response = Agent::using(OpenRouter::class)
    ->withKey("")
    ->model('openrouter/free')
    ->prompt('Hello !')
    ->send();

Doc : doppar/docs#38

I bumped symfony/ai versions also

[techmahedy]

@rrr63 great job, you can merge and release.

[techmahedy]

@rrr63 great job, you can merge and release.