[Dynamic workflow configs] Form error in add video page: element already exists

[ferishili]

The new feature that provides the dynamic workflow config panel to the teacher to pass their desired settings works fine until there is a same named element to be added to the add video form. In this case the moodle throws an error, complainin about "element already exists".
For my case (need to say that it is rare because I was adding this for testing), the same element was startDate. This is not common case, but we have to prevent this issue.

Here is a portion of how the error looks like!

[ferishili]

This will be fixes together via #405