Add context filter to VectorPayload

[ronal2do]

based on this issue #91

Context

As a user I want to be able to use filter operations when using my chat

const result = await ragChat.chat<{ unit: string }>("Where is the capital of Japan?", {
    namespace,
    contextFilter: "unit = 'Samurai'",
});

Reference

https://upstash.com/docs/vector/features/filtering#metadata-filtering

[CahidArda]

Thanks a lot for the contributions @ronal2do!

It looks like the CIs can't run because your fork can't access the secrets we use in the CIs.

In order to use the secrets, we would need to update our CI. We would like to do this later.

In order to continue, we will close the PRs (this and #93) and open new ones with your commits.

Again, thanks a lot for the contributions!