Support multiple values(list type) in expression field of powerbi table

[harshsoni2024]

Is your feature request related to a problem? Please describe. ingestion fails with a pydantic validation error for PowerBiTable due to expression field type mismatch. In my case, the expression is an array of strings, but the ingestion model expects a single string. logs:

pydantic_core._pydantic_core.ValidationError: 307 validation errors for PowerBiTable
measures.0.expression
  Input should be a valid string [type=string_type, input_value=['', 'MASKED', 'MASKED'], input_type=list]
measures.0.isHidden
  Field required [type=missing, input_value={'name': 'MASKED', 'MASKED'}, input_type=dict]

Describe the solution you'd like The ingestion process should handle expression fields that are arrays (multi-line measures) gracefully—either by joining them into a string or updating the schema to accept arrays.