Add serialized_attr for LTI rostering opt-out

[carl-codeorg]

Adds a new serialized_attr to the user model for the roster sync opt-out setting. Also adds a helper to the LTI policy to check this field. This is prerequisite work for adding this setting to the account settings page and sync confirmation pop-up.

Links

Jira ticket

Testing story

Deployment strategy

Follow-up work

Adding toggle to Account Settings page
Adding button to sync pop-up

Privacy

Security

Caching

PR Checklist:

• Tests provide adequate coverage
• Privacy and Security impacts have been assessed
• Code is well-commented
• New features are translatable or updates will not break translations
• Relevant documentation has been added or updated
• User impact is well-understood and desirable
• Pull Request is labeled appropriately
• Follow-up work items (including potential tech debt) are tracked and linked

[wilkie]

Can't really go wrong, here. :) 👍