[FEATURE] Add capabiliy to modify the used HTTP Client

[foppelfb]

Tasks:

• Add httpClient option to the ProviderConfiguration
• Inject the httpClient into the Bridge Factory
• Add Documentation
• Add Unittests

Resolves: #33
Releases: main

[o-ba]

Hey @foppelfb and thanks a lot for working on this!

The use case makes total sense, and I'd like to get it in. But I ran into a few things with the current approach that I don't think we can fix with small tweaks.

The main problem is that setting the client on ProviderConfiguration from a middleware doesn't reliably reach the request:

• The adapter caches the platform per configuration, so whichever call creates it first wins. If the connection check or the grading judge happens to run first in a process, your middleware's client is never used.

• Fallback providers, smart routing and auto model switch all work with their own ProviderConfiguration instances, which don't carry the client. So the retry after a timeout, probably the case you care about most, would run with the default timeout again.

I'm also not too happy about having a Symfony type on ProviderConfiguration. AiM doesn't require symfony/http-client-contracts, and I'd rather not add that dependency for everyone just because Symfony AI is optional.

What do you think about going with your "Alternative 1" instead? A PSR-14 event in SymfonyAiPlatformAdapter, fired when the platform is built, with the configuration and a settable client. It runs exactly where the client matters, it covers fallbacks and rerouting automatically, and the Symfony types stay in the Symfony AI part of the code.

A few smaller things:

• Only dispatch the event (and pass httpClient) if the bridge factory actually declares that parameter; we already reflect endpoint and apiKey the same way.
• Since the platform is cached per configuration, the event fires once per provider record. Worth a sentence in the docs so nobody expects per-request control.
• A test that goes through the adapter would be great: a listener sets a client, and the factory receives it.