[Platform] Add grok AI and its model

[Solirio]

Hello,

I would love to see GrokAi implemented in Symfony Ai since it is currently performing well on a lot of benchmark and also with very good cost/quality ratio.

Thanks in advance.

[OskarStark]

Open for a PullRequest?

[valtzu]

You can already use Grok with OpenResponses bridge, see #2381 / #2382 for example.