[C2] Webservices for user progress tracking

[ywarnier]

The new API should include:

• a service to get the average learning paths progress of one user in one course/session (-> /users/{id}/courses/{courseId}/stats/avg-lp-progress)
• a service to get the certificates of a user in one course/session (-> /users/{id}/courses/{courseId}/stats/certificates)
• a service to get the global score of a gradebook of a user in one course/session (-> /users/{id}/courses/{courseId}/stats/gradebook-global)
• a service to get the average score in a course/session (across all users) (-> /courses/{id}/stats/course-avg-score)
• a service to get the average progress in a course/session (across all users) (-> /courses/{id}/stats/course-avg-progress)

This is to provide equivalent services to what we have in 1.11

[christianbeeznest]

It is added in this PR #6624

Thanks for confirmation.

[ywarnier]

Code looks good to me.
Is there a way to add these new services to the /api route generated by ApiPlatform?