Allow to specify source database instead of defaulting to bronze database in __get_silver_dataflow_spec_dataframe

[rtdtwo]

Issue

The FAQs describes that any data source can be used for silver tables. However, the code always tries to find the bronze database from the onboarding rows, and there's no explicit mention of a source database other than a bronze database.

Fix

Change the code to accomplish the following:

• Use bronze_database_{env} if the field is found in onboarding rows.
• If not, find and use source_details.

[codecov[bot]]

Codecov Report

Attention: 3 lines in your changes are missing coverage. Please review.

Comparison is base (2a93dd9) 90.28% compared to head (f4fbd2b) 89.95%.

Files	Patch %	Lines
src/onboard_dataflowspec.py	40.00%	1 Missing and 2 partials :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #34      +/-   ##
==========================================
- Coverage   90.28%   89.95%   -0.34%     
==========================================
  Files           8        8              
  Lines         803      806       +3     
  Branches      149      151       +2     
==========================================
  Hits          725      725              
- Misses         31       32       +1     
- Partials       47       49       +2     

Flag	Coverage Δ
unittests	89.95% <40.00%> (-0.34%)	:arrow_down:

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[ravi-databricks]

@rtdtwo, Needs to add unit tests for added new lines as per above code coverage report.

[ravi-databricks]

Closing this PR since its very old and author did not followup on review changes.