SNOW-702210: Node.js Connector => How to fetchAsString but keep null values

[sfc-gh-ext-simba-jy]

Description

Please explain the changes you made here.

• Added 'Null' option in the fetchAsString list. This change will be the BCR. If the customer wants to get the value 'null' as String 'NULL', they should add the 'NULL' in the fetchAsString option.

Checklist

• Format code according to the existing code style (run npm run lint:check -- CHANGED_FILES and fix problems in changed code)
• Create tests which fail without the change (if possible)
• Make all tests (unit and integration) pass (npm run test:unit and npm run test:integration)
• Extend the README / documentation and ensure is properly displayed (if necessary)
• Provide JIRA issue id (if possible) or GitHub issue id in commit message

[codecov]

Codecov Report

Attention: Patch coverage is 84.21053% with 3 lines in your changes are missing coverage. Please review.

Project coverage is 89.24%. Comparing base (e80f3ea) to head (e4817eb).

Files	Patch %	Lines
lib/connection/connection_config.js	75.00%	1 Missing ⚠️
lib/connection/result/column.js	87.50%	1 Missing ⚠️
lib/connection/result/data_types.js	80.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #831      +/-   ##
==========================================
- Coverage   89.25%   89.24%   -0.02%     
==========================================
  Files          61       61              
  Lines        5892     5903      +11     
==========================================
+ Hits         5259     5268       +9     
- Misses        633      635       +2     

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[ghost]

@sfc-gh-ext-simba-jy Please add test cases to cover the use case of keeping old behavior.

[sfc-gh-pmotacki]

LGTM