Migrate non-GitHub fields from `github.User` to `owasp.MemberProfile`

**Is your feature request related to a problem? Please describe.**

We originally stored several OWASP-specific fields inside the github.User model, even though they were not GitHub-related. Now that we’ve introduced the owasp.MemberProfile model, we should migrate this data to its proper location.

**Describe the solution you'd like**

The following fields should be moved from github.User → owasp.MemberProfile:

- has_public_member_page
- is_owasp_staff
- contributions_count

Implement a multi-step migration process:

1. **Add new fields to `owasp.MemberProfile` and migrate existing data**

* Ensure all related logic continues to work without interruption.
* Maintain backwards compatibility during the transition.
2. **Remove the old fields from `github.User` in a separate PR** once everything is stable.
* Add or update **tests** to cover:

* Data migration.
* Model behavior.
* Any views, serializers, or business logic relying on these fields.
* Verify that all existing features using these fields continue to work correctly after the migration.

**Are you going to work on implementing this?**

- [ ] Yes
- [x] No