Rename the QdrantRetriever + /retrievers folder

[bilgeyucel]

Is your feature request related to a problem? Please describe.
As a user, I'd like to have predictable names for components and other retriever names contain the retrieval method

Describe the solution you'd like
Renaming the QdrantRetriever as QdrantEmbeddingRetriever to align with the current convention. Also, since we foresee QdrantSparseRetriever and QdrantHybridRetriever, it makes sense to create a new retrievers folder and move QdrantEmbeddingRetriever into it.

Describe alternatives you've considered
N/A

Additional context
N/A

[sahusiddharth]

@bilgeyucel

Can you please confirm?

Things to do:-

• Rename the current [QdrantRetriever](https://github.com/deepset-ai/haystack-core integrations/blob/main/integrations/qdrant/src/qdrant_haystack/retriever.py#L9) to QdrantEmbeddingRetriever.
• Create a new folder named retriever inside src/qdrant_haystack and put retriever.py inside it.

[sahusiddharth]

Hi @silvanocerza , I hope you're doing well. I noticed that the issue is still open. Could you please provide an update on its status?

[silvanocerza]

@sahusiddharth this can be closed I think, I left it open cause it was also about adding a new retrievers folder but we've done that with #255.

I'll close it as done. Thanks for pinging. 🙏