Add ability to complete course in student management without removing and readding

[dericleeyy]

Is your feature request related to a problem? Please describe

Currently, the only way to help a student complete a course in student management is to remove and readd them with the complete course option.

Describe the solution you'd like

Add a new action to mark students as Complete Course.

Additional context

Created from https://wordpress.org/support/topic/mark-a-course-complete-in-learner-management/

[hannahmwool]

Would love this feature to be included. In the meantime I am planning to build a function to try and achieve this. Thanks!