feat: can-redeem user message for no/cancelled/errored assignments

[iloveagent57]

ENT-8114 | The can-redeem endpoint now returns a reason and user message related to policies that are unredeemable due to a lack of allocated LearnerContentAssignment record for the requesting user, or the existence of an assignment in a CANCELLED or ERRORED state.

Sample response payload for my local policy that does not have an assignment for the requesting test user:

[
    {
        "content_key": "course-v1:edX+DemoX+Demo_Course",
        "list_price": null,
        "redemptions": [],
        "has_successful_redemption": false,
        "redeemable_subsidy_access_policy": null,
        "can_redeem": false,
        "reasons": [
            {
                "reason": "reason_learner_not_assigned_content",
                "user_message": "You can't enroll right now because this course is not assigned to you.",
                "policy_uuids": [
                    "3cc0ad2c-ede1-476c-8271-97683855e41d"
                ],
                "metadata": {
                    "enterprise_administrators": [
                        {
                            "email": "[email protected]",
                            "lms_user_id": 145
                        }
                    ]
                }
            }
        ]
    }
]

Assignment does not exist:

Assignment exists but canceled

Errored assignment

I re-used the "no assignment exists" message here, since there was no pre-defined spec for the message to show in this case. This is still better than the current state of things, where we'd show a message about a missing code if the requesting learner had an errored assignment for the requested content.

[adamstankiewicz]

nit/typo:

Suggested change

	# Only an erroed assignment exists.
	# Only an errored assignment exists.

[adamstankiewicz]

@iloveagent57 Just to verify/confirm, there were no associated changes necessary in frontend-app-learner-portal-enterprise to ensure the message appears and/or the "Contact administrator" CTA appears?

[iloveagent57]

Correct, no local changes to the learner-portal required to get those screenshots as above.