Idea: date custom variable

[DavidWells]

Inspo: https://github.com/aws-cloudformation/aws-cloudformation-templates/blob/690d970adf7b850fb2c4f686b450ef1a1af4e563/CloudFormation/MacrosExamples/DateFunctions/handler.py

${date('2024-01-19', 'Add 30days')}

Resources:
  ExpiryDate:
    Type: Custom::Date
    Properties:
      Operation: Add
      Date: '2024-01-19'
      Days: 30
    # Transformed to: '2024-02-18'

  DaysBetween:
    Type: Custom::Date
    Properties:
      Operation: Days
      Date: '2024-01-19'
      Date2: '2023-12-19'
    # Transformed to: '31'

[DavidWells]

Dupe https://github.com/DavidWells/configorama/issues/6