refactor: use MongoDB singleton for connection management

[kom-senapati]

• What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)

Adds a file core/mongo_db.py for the singleton class of pymongo client which is used to get connections across all files and no extra connection is created.

• Why was this change needed? (You can also link to an open issue here)

Closes #1170

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Name	Status	Preview	Comments	Updated (UTC)
docs-gpt	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Oct 31, 2024 11:34am

[dartpain]

Hey please check the imports and test the application.
Thank you

[kom-senapati]

I had tested it locally before doing PR

[dartpain]

It seems like tests are failing for it:
https://github.com/arc53/DocsGPT/actions/runs/11397141420/job/31712108327?pr=1335

______________________ ERROR collecting tests/test_app.py ______________________
ImportError while importing test module '/home/runner/work/DocsGPT/DocsGPT/tests/test_app.py'.
Hint: make sure your test modules/packages have valid Python names.
Traceback:
/opt/hostedtoolcache/Python/3.11.10/x[64](https://github.com/arc53/DocsGPT/actions/runs/11397141420/job/31712108327?pr=1335#step:5:65)/lib/python3.11/importlib/__init__.py:126: in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
tests/test_app.py:3: in <module>
    from application.api.answer.routes import answer
application/api/answer/routes.py:14: in <module>
    from core.mongo_db import MongoDB
E   ModuleNotFoundError: No module named 'core'
=============================== warnings summary ===============================
../../../../../opt/hostedtoolcache/Python/3.11.10/x64/lib/python3.11/site-packages/flask_restx/api.py:19
../../../../../opt/hostedtoolcache/Python/3.11.10/x64/lib/python3.11/site-packages/flask_restx/api.py:19
  /opt/hostedtoolcache/Python/3.11.10/x64/lib/python3.11/site-packages/flask_restx/api.py:19: DeprecationWarning: jsonschema.RefResolver is deprecated as of v4.18.0, in favor of the https://github.com/python-jsonschema/referencing library, which provides more compliant referencing behavior as well as more flexible APIs for customization. A future release will remove RefResolver. Please file a feature request (on referencing) if you are missing an API for the kind of customization you need.
    from jsonschema import RefResolver

-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html

---------- coverage: platform linux, python 3.11.10-final-0 ----------
Coverage XML written to file coverage.xml

=========================== short test summary info ============================
ERROR tests/llm/test_anthropic.py
ERROR tests/llm/test_openai.py
ERROR tests/llm/test_sagemaker.py
ERROR tests/test_app.py
!!!!!!!!!!!!!!!!!!! Interrupted: 4 errors during collection !!!!!!!!!!!!!!!!!!!!
======================== 2 warnings, 4 errors in 6.[82](https://github.com/arc53/DocsGPT/actions/runs/11397141420/job/31712108327?pr=1335#step:5:83)s =========================

[codecov]

Codecov Report

Attention: Patch coverage is 86.95652% with 3 lines in your changes missing coverage. Please review.

Project coverage is 34.00%. Comparing base (355fd2b) to head (82189b0).
Report is 232 commits behind head on main.

Files with missing lines	Patch %	Lines
application/core/mongo_db.py	78.57%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1335      +/-   ##
==========================================
+ Coverage   32.93%   34.00%   +1.06%     
==========================================
  Files          62       68       +6     
  Lines        3112     3347     +235     
==========================================
+ Hits         1025     1138     +113     
- Misses       2087     2209     +122     

☔ View full report in Codecov by Sentry.
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[dartpain]

LGTM, thank you!