Implement generic filtering of the entries

[kacperlukawski]

As requested in #20 and in some conversations, the find method should allow for filtering entries by their metadata. For example, if we use Cursor and store code snippets using different languages, filters could help to not include Rust in Python projects and vice versa.

[4141done]

Having just engaged with the tool and wished for this - cool to see it filed. I'm still learning, but as a configuration option I wonder whether it would make sense to allow the server to be configured to constrain the fields/shape of metadata we ask the LLM to include in the query to be either:

• A predefined shape we specify in the config
• Some set of fields and values the server can derive from the target collection.

That way I can be sure I'm segregating the similarity search on the specific elements of the metadata that matter to me.
As I said I'm still learning so also happy to told where I'm misunderstanding 😅