feat: Support for userCol and itemCol as string types in SAR model

[dciborow]

Fixes #2275

Add support for userCol and itemCol as string types in the SAR model.

• Python Files:

  • Add core/src/main/python/synapse/ml/recommendation/SAR.py to handle string userCol and itemCol.
  • Modify core/src/main/python/synapse/ml/recommendation/SARModel.py to handle string userCol and itemCol in the recommendForUserSubset function.

• Scala Files:

  • Modify core/src/main/scala/com/microsoft/azure/synapse/ml/recommendation/SAR.scala to handle string userCol and itemCol in the calculateUserItemAffinities and calculateItemItemSimilarity functions.
  • Modify core/src/main/scala/com/microsoft/azure/synapse/ml/recommendation/SARModel.scala to handle string userCol and itemCol.

• Tests:

  • Update core/src/test/python/synapsemltest/recommendation/test_ranking.py to include tests for string userCol and itemCol.
  • Update core/src/test/scala/com/microsoft/azure/synapse/ml/recommendation/SARSpec.scala to include tests for string userCol and itemCol.

• Documentation:

  • Update docs/Quick Examples/estimators/core/_Recommendation.md to include examples with string userCol and itemCol.

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