Instrument new LangChain vectorstores and pin langchain to 0.1.16.

[umaannamalai]

This PR adds support for 3 new vectorstores supported by LangChain. It also pins LangChain to an older version while we add support for v0.1.17.

[github-actions]

🦙 MegaLinter status: ✅ SUCCESS

Descriptor	Linter	Files	Fixed	Errors	Elapsed time
✅ PYTHON	bandit	2		0	5.74s
✅ PYTHON	black	3	0	0	2.1s
✅ PYTHON	flake8	3		0	1.26s
✅ PYTHON	isort	3	0	0	0.36s
✅ PYTHON	pylint	3		0	8.27s

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[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.62%. Comparing base (8b9e394) to head (76132e6).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1134      +/-   ##
==========================================
+ Coverage   79.91%   81.62%   +1.71%     
==========================================
  Files         192      192              
  Lines       21301    21304       +3     
  Branches     3706     3706              
==========================================
+ Hits        17022    17390     +368     
+ Misses       3222     2835     -387     
- Partials     1057     1079      +22     

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