feat: add support for custom headers

[hsm207]

allow users to specify additional headers they want to pass when sending
requests to the weavate server

Related Issues

• fixes Weaviate: Allow custom HTTP headers to pass to weaviate client #3916

Proposed Changes:

Add additional_headers parameter to the weaviate document store's constructor. This parameter contains a dictionary of headers that the weaviate client will pass to the weaviate server each time a request is time.

For example, users can pass their OpenAI key using:

additional_headers = {'X-OpenAI-Api-Key': 'KEY'}

How did you test it?

I'm not sure how to test this. Please advise.

Notes for the reviewer

Should we remove the raise NotImplementedError("WeaviateDocumentStore does not support headers.") and replace with a warning message saying that the headers will be ignored because in weaviate, the headers are configured when the client is initialized, not when a query is made.

Checklist

• I have read the contributors guidelines and the code of conduct
• I have updated the related issue with new insights and changes
• I added tests that demonstrate the correct behavior of the change
• I've used one of the conventional commit types for my PR title: fix:, feat:, build:, chore:, ci:, docs:, style:, refactor:, perf:, test:.
• I documented my code
• I ran pre-commit hooks and fixed any issue

[vblagoje]

LGTM, let's just wait for another CI run