Migrate null values for users.private_profile column

What does this MR do?

This MR migrates null values to false for the private_profile column within the users table.

Issue: https://gitlab.com/gitlab-org/gitlab-ce/issues/57538

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content - https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/14300