add_field, remove_field, rename_field blocks - support list

[spicy-sauce]

Instead of defining multiple blocks for adding new fields, for example, support this format too (list)

  - uses: add_field
    with:
      - field: BillingHouseNumber
        expression: split(`BillingAddress`,'.')[0]
      - field: BillingStreet
        expression: split(`BillingAddress`,'.')[1]
      - field: BillingCountry
        expression: upper(`BillingCountry`)
      - field: VAT
        expression: total * 1.17
        language: sql

The other format should be also supported for dealing with only one field:

  - uses: add_field
    with:
        field: BillingHouseNumber
        expression: split(`BillingAddress`,'.')[0]