Allow use of ui-kit icons on secondary button of CustomFormModalPage

[dogayuksel]

Problem

We would like to standardize save/cancel behavior across Merchant Center. Forms used for editing existing items should have a 'revert changes' button as a secondary action to cancel the changes. Forms used for adding new items should continue to use 'cancel'.

Revert changes button should ideally have the 'revert' icon.

See UI-Team meeting notes for details: https://wiki.commercetools.com/pages/viewpage.action?pageId=193308973

See priceless issue for more details on the dependent task: https://jira.commercetools.com/browse/PRC-1261

Suggested Solution

As secondary button of ui-kit already supports iconLeft property, we should modify CustomFormModalPage to optionally accept it and pass it down.

Alternative Solution

Use ui-kit's secondaryButton instead the secondary button exposed by the CustomFormModalPage. However it would be cleaner to use the icon feature through the interface of CustomFormModalPage component.

[anilkk]

@dogayuksel We appreciate your suggestion to improve the UX of CustomFormModalPage. We are working on defining the review process and guidelines for the contributions. We have to wait until a well-defined review process in place before we involve our UX designers to review.

[mmaltsev-ct]

@FilPob could you revisit the issue please, and check whether the UX team wants to have such functionality as standard behavior.