Add completion API specs and update enrolment method

[MyDrift-user]

Type of Change

• New feature
• Hotfix

Description

• JSON specs for course and activity completion endpoints under Completion.
• Updated enrol_self_enrol_user.json to use POST and clarified its description.
• Added ALLOW_ORIGINS and LOG_LEVEL environment variables to compose.yaml.

Testing

• testet, works

Additional Information

• manual course completion or course status must be configured per course

Checklist

• My code adheres to the coding and style guidelines of the project.
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• I have made corresponding changes to the documentation.
• My changes generate no errors/warnings/merge conflicts.