As a user, I can configure additional columns to Test Step specifications

A user must be able to configure an additional column(s) for manual Test Steps as a means to provide additional and clearly identified data that may be relevant for the context of each step.

These additional columns will be defined as Test Step "custom fields" at the project level, so that users can define their values during the specification (in the Test issue screen; not on the execution screen) on each Test case. 

It should be possible to create, in the project settings, Test Step custom field types of string, number, date, boolean, multi-select, single-select and user.
It should be possible to define a Test Step custom field as mandatory to be filled or not