Ability to set custom input as a error target

[patryk-smc]

We want our custom input to enter an error state if it fails validation with the Checkout Validation Function.

For example:

<Checkbox id="mandatory_checkbox">Mandatory checkbox</Checkbox>

FunctionRunResult:

    [
      {
        localizedMessage: "This checkbox is mandatory",
        target: "$.mandatory_checkbox",
      },
    ];

[gil--]

Would love to see this as well to ensure checkout is blocked for required non-native fields.