Allow members to join multiple cohorts of the same course

Allow Members to Access Multiple Cohorts of the Same Course Simultaneously

Introduce a setting or permission structure that allows returning members (e.g., from past cohorts) to join and view a new course cohort without losing access to their original/past cohort space. Currently, Heartbeat restricts a member's view to a single cohort, meaning that if a member wants to participate in an updated course run, administrators are forced to move them out of their previous cohort group, overwriting their historic access. Grant access to concurrent or multiple cohorts of the same course so members can reference past materials while engaging with new ones.