feat: Part 3 - Introduce Vector Store Manager and Vector Store Class

[ishaansehgal99]

Reason for Change:
This series of PR will integrate llamaindex RAG service for Kaito.

This PR introduces the main logic for indexing, querying, adding and listing documents.faiss_store.py is the most important file.

faiss_store.py introduces the code to perform RAG operations, including persisting and loading DB from disk incase it is needed. PR also includes tests for faiss_store.py in test_faiss_store.py. conftest.py is a test configuration file, in it we ensure the tests run synchronously and CPU only.

manager.py is a light abstraction around the API (main.py) which will be introduced in subsequent PRs.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 54.45%. Comparing base (5c30038) to head (457c8ec).
Report is 38 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #633      +/-   ##
==========================================
- Coverage   58.18%   54.45%   -3.74%     
==========================================
  Files          30       34       +4     
  Lines        2987     3928     +941     
==========================================
+ Hits         1738     2139     +401     
- Misses       1149     1683     +534     
- Partials      100      106       +6     

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