Change default visibility level for FogBugz imported projects to Private

What does this MR do?

Internal visibility has been restricted on GitLab.com https://gitlab.com/gitlab-org/gitlab-ee/issues/12388 Currently FogBugz importer fails with an error message An error occurred while importing project: Visibility level internal has been restricted by your GitLab administrator because by default all FogBugz projects are set visibility level Internal, which is now restricted.

Setting visibility level to Private to unblock imports from FogBugz.

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry for user-facing changes, or community contribution. Check the link for other scenarios.
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Performance and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team