TYPO3 ext_form custom form element configuration including validators

configuration.yaml

            FirstName:
              __inheritances:
                10: 'TYPO3.CMS.Form.prototypes.standard.formElementsDefinition.Text'
              renderingOptions:
                templateName: 'Text'
              label: 'Custom First Name'
              defaultValue: ''
              properties:
                fluidAdditionalAttributes:
                  placeholder: 'Insert custom first name'
                  required: required
                  minlength: '1'
                  maxlength: '20'
              validators:
                -
                  identifier: StringLength
                  options:
                    minimum: '1'
                    maximum: '20'
                -
                  identifier: NotEmpty

formDefinition.yaml

      -
        type: FirstName
        identifier: firstname