Rename add_users_to_scope to reflect enroll + auto-assign role

add_users_to_scope actually enrolls users into a scope and grants auto-assign roles; rename it to reflect that and update all call sites. Low-priority cleanup noted in BEP-1062 (#12842) section 2.3/2.7.

Success Criteria
- [ ] add_users_to_scope renamed to reflect what it does (enroll + auto-assign role); all call sites updated
- [ ] pants test passes for affected packages

JIRA Issue: BA-6879

Search the Python repository for the add_users_to_scope entry point and every call site, then read the surrounding implementation to confirm its enrollment and auto-assign role behavior. Update the name consistently and run pants test for the affected packages; done means all references use the new name and the tests pass.

Written by the indexing model from the issue text.