Deprecate \Drupal\ai\AiVdbProviderInterface::getConfig()

Thanks makes sense. I think we might need to target 2.0 though to be able to have the VDB Providers separately lock in to earlier/later versions, but will start a slack thread discussion because there seems to be several issues in the queue that change the interfaces/methods so will get confusing talking about it in multiple issues.

Actually this is fine, given its experimental and it seems of those listed on AI module homepage, only Pinecone and Milvus are actively supported VDB providers (checked and Azure & SQLlite & Postgres) and they seem to lock to old AI core versions, and they continue to work fine since they extend AiVdbProviderClientBase.

Unless someone else has concerns, we can merge this.