ui4t updates

[Ishankoradia]

• add support for data type for postgres
• add support for data type for bigquery
• Merge operations cte fixes; the operation doesn't output the correct cte.
• update the merge operation to take input either as a source or a model. Currently it assumes the input to be a source.
• _sql function of each operation needs to return the output columns also now. Update merge_operation accordingly.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 92.10526% with 9 lines in your changes are missing coverage. Please review.

Project coverage is 81.61%. Comparing base (5f54d62) to head (2905745).

Files	Patch %	Lines
dbt_automation/operations/flattenjson.py	0.00%	7 Missing ⚠️
dbt_automation/operations/mergeoperations.py	93.75%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #64      +/-   ##
==========================================
+ Coverage   81.55%   81.61%   +0.05%     
==========================================
  Files          22       22              
  Lines         949      952       +3     
==========================================
+ Hits          774      777       +3     
  Misses        175      175              

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