[LTI Provider] Improve logging in send_composite_outcome Celery task

Problem

The send_composite_outcome Celery task currently produces minimal log output. On success, only the generic Celery trace log is emitted — no context about what grade was sent, to whom, or for which user/course/assignment.

Current log output (on success):

Task lms.djangoapps.lti_provider.tasks.send_composite_outcome[<task-id>] succeeded in 2.3s: None

This makes it difficult to:

• Confirm which grade value was actually sent to the LTI consumer
• Identify which user or course/assignment was involved
• Diagnose failures without external timestamps (e.g., checking Canvas directly)

Suggested Improvements

Add structured log statements inside send_composite_outcome (and related tasks) that include:

1. User identifier — whose grade is being sent (user ID or anonymized ID)
2. Course and usage key — which course/assignment triggered the passback
3. Grade value — the score being submitted (e.g., 0.85)
4. LTI outcome URL — the endpoint on the consumer side receiving the grade
5. Result on failure — HTTP status code, response body, or exception detail

Expected Benefit

Operators and support teams can confirm grade passback without needing Canvas-side investigation. Failures become immediately diagnosable from logs alone.

Files Likely Involved

• lms/djangoapps/lti_provider/tasks.py
• lms/djangoapps/lti_provider/outcomes.py

Start in lms/djangoapps/lti_provider/tasks.py at send_composite_outcome, then read lms/djangoapps/lti_provider/outcomes.py to trace the grade passback and related tasks. Done means successful and failed submissions emit structured logs containing the requested user, course/usage key, grade, outcome URL, and failure details.