Allow declaring control options

[philippjfr]

Make it possible to set explicit options for controls or resolve options by reference:

transforms:
  - type: custom
    controls:
       - name: some_parameter
         options: ['A', 'B', 'C']

We can also use references to resolve categorical column values:

transforms:
  - type: custom
    controls:
       - name: some_parameter
         options: @some_source.some_table.some_categorical_field

[github-actions]

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