Snow-802269 Add JsonNode function to read variant column as json object

[sfc-gh-gmahadevan]

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1. What GitHub issue is this PR addressing? Make sure that there is an accompanying issue to your PR.

   Fixes #802269

2. Fill out the following pre-review checklist:

   • [X] I am adding a new automated test(s) to verify correctness of my new code
   • [ ] I am adding new logging messages
   • [ ] I am adding a new telemetry message
   • [ ] I am adding new credentials
   • [ ] I am adding a new dependency

3. Please describe how your code solves the related issue.

   add toJsonNode function so a variant column can be read as json without converting to string first

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• [X] This change has passed precommit
• [ ] I have reviewed code coverage report for my PR in (Sonarqube)