Spring-ai Remove client and embedding from package name for ChatClient and EmbeddingClient implementations

The model provider implementing class will live under org.springframework.ai.huggingface and not org.springframework.ai.huggingface.client for example.

The reason is that otherwise we end up with packages that have one class in them.

Places to change are.

• org.springframework.ai.huggingface.client.HuggingfaceChatClient
• org.springframework.ai.openai.client.OpenAiChatClient and org.springframework.ai.openai.embedding.OpenAiEmbeddingClient
• org.springframework.ai.vertex.generation.VertexAiChatClient and org.springframework.ai.vertex.embedding.VertexAiEmbeddingClient

Remember to update any docs.