Add auto_ssl_enabled to pages domains

What does this MR do?

https://gitlab.com/gitlab-org/gitlab-ce/issues/28996

Just adds auto_ssl_enabled to pages domains This field will indicate if we should obtain Let's Encrypt ssl certificate for domain

It will be used in https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/26438

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• 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.