[AiBundle] Use model FQCN for indexer config, to allow any Symfony\AI\Platform\Model child class

[welcoMattic]

Q	A
Bug fix?	yes
New feature?	no
Docs?	no
Issues	Fix #59
License	MIT

Before:

ai:
    indexer:
        default:
            platform: 'symfony_ai.platform.mistral'
            model:
                name: 'Embeddings'
                version: 'mistral-embed'

After

ai:
    indexer:
        default:
            platform: 'symfony_ai.platform.mistral'
            model:
                name: 'Symfony\AI\Platform\Bridge\Mistral\Embeddings'
                version: 'mistral-embed'

This way, any class extending Symfony\AI\Platform\Model can be used as embedder model, even one written by users themselves.
Embeddings model of providers (OpenAI, Mistral, Gemini, ...) can be named Embeddings with no issue.

---

Replace php-llm/llm-chain-bundle#99

[welcoMattic]

Repost original comment from @chr-hertel (php-llm/llm-chain-bundle#99 (comment)):

Yup, that first implementation was def too stupid, true. And I guess the className thing is something that should be supported - especially when you thin about user land model classes for example.

However, looking at this config:

llm_chain:
    embedder:
        default:
            platform: 'llm_chain.platform.mistral'
            model:
                name: 'PhpLlm\LlmChain\Platform\Bridge\Mistral\Embeddings'
                version: 'mistral-embed'

This is a bit redundant, right? the service llm_chain.platform.mistral would anyways only support one embeddings class - I think we could also solve that by the Platform exposing which models (and their names) it would support. so that we would basically only chose from a subset of those classes.

WDYT?

[chr-hertel]

Yes, let's do this to unblock the usage for now - we can work on a slimmer config as a next step.

[chr-hertel]

Let's break it once for both parameters and also the agent config - same issue.

What do you think about?

• class instead of name or className
• name instead of version (also rather deprecated)

and I guess the docs and demo need an update as well here

[chr-hertel]

Conflicts after merging #94, but rebase should do the trick hopefully