CE to EE guide for 11.2

What does this MR do?

Creates the CE to EE guide for 11.2

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• Conforms to the code review guidelines
  • Has been reviewed by a Backend maintainer(https://docs.gitlab.com/ee/development/merge_request_performance_guidelines.html)
• Conforms to the style guides

Related to:

gitlab-org/release/tasks#377 (closed)