Use Block Hooks to inject the View Certificate button into the Course Completed page

[donnapep]

Is your feature request related to a problem? Please describe

We currently use the sensei-lms.Course.completedActions hook to add the View Certificate button to the Course Completed page. Block Hooks are a better / simpler way to do this.

Describe the solution you'd like

Add the View Certificate button to the Course Completed page (editor and frontend) using Block Hooks.

Describe alternatives you've considered

Doing nothing given that we have plans to move Certificates functionality right into Sensei. However, those plans are on hold at this time.